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<li><span class="stability_2"><a href="#assert">Assert</a></span>
<ul>
<li><a href="#strict-assertion-mode">Strict assertion mode</a></li>
<li><a href="#legacy-assertion-mode">Legacy assertion mode</a></li>
<li><a href="#class-assertassertionerror">Class: assert.AssertionError</a>
<ul>
<li><a href="#new-assertassertionerroroptions"><code>new assert.AssertionError(options)</code></a></li>
</ul>
</li>
<li><span class="stability_0"><a href="#class-assertcalltracker">Class: <code>assert.CallTracker</code></a></span>
<ul>
<li><a href="#new-assertcalltracker"><code>new assert.CallTracker()</code></a></li>
<li><a href="#trackercallsfn-exact"><code>tracker.calls([fn][, exact])</code></a></li>
<li><a href="#trackergetcallsfn"><code>tracker.getCalls(fn)</code></a></li>
<li><a href="#trackerreport"><code>tracker.report()</code></a></li>
<li><a href="#trackerresetfn"><code>tracker.reset([fn])</code></a></li>
<li><a href="#trackerverify"><code>tracker.verify()</code></a></li>
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<li><a href="#assertvalue-message"><code>assert(value[, message])</code></a></li>
<li><a href="#assertdeepequalactual-expected-message"><code>assert.deepEqual(actual, expected[, message])</code></a>
<ul>
<li><a href="#comparison-details">Comparison details</a></li>
</ul>
</li>
<li><a href="#assertdeepstrictequalactual-expected-message"><code>assert.deepStrictEqual(actual, expected[, message])</code></a>
<ul>
<li><a href="#comparison-details_1">Comparison details</a></li>
</ul>
</li>
<li><a href="#assertdoesnotmatchstring-regexp-message"><code>assert.doesNotMatch(string, regexp[, message])</code></a></li>
<li><a href="#assertdoesnotrejectasyncfn-error-message"><code>assert.doesNotReject(asyncFn[, error][, message])</code></a></li>
<li><a href="#assertdoesnotthrowfn-error-message"><code>assert.doesNotThrow(fn[, error][, message])</code></a></li>
<li><a href="#assertequalactual-expected-message"><code>assert.equal(actual, expected[, message])</code></a></li>
<li><a href="#assertfailmessage"><code>assert.fail([message])</code></a></li>
<li><span class="stability_0"><a href="#assertfailactual-expected-message-operator-stackstartfn"><code>assert.fail(actual, expected[, message[, operator[, stackStartFn]]])</code></a></span></li>
<li><a href="#assertiferrorvalue"><code>assert.ifError(value)</code></a></li>
<li><a href="#assertmatchstring-regexp-message"><code>assert.match(string, regexp[, message])</code></a></li>
<li><a href="#assertnotdeepequalactual-expected-message"><code>assert.notDeepEqual(actual, expected[, message])</code></a></li>
<li><a href="#assertnotdeepstrictequalactual-expected-message"><code>assert.notDeepStrictEqual(actual, expected[, message])</code></a></li>
<li><a href="#assertnotequalactual-expected-message"><code>assert.notEqual(actual, expected[, message])</code></a></li>
<li><a href="#assertnotstrictequalactual-expected-message"><code>assert.notStrictEqual(actual, expected[, message])</code></a></li>
<li><a href="#assertokvalue-message"><code>assert.ok(value[, message])</code></a></li>
<li><a href="#assertrejectsasyncfn-error-message"><code>assert.rejects(asyncFn[, error][, message])</code></a></li>
<li><a href="#assertstrictequalactual-expected-message"><code>assert.strictEqual(actual, expected[, message])</code></a></li>
<li><a href="#assertthrowsfn-error-message"><code>assert.throws(fn[, error][, message])</code></a></li>
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<details role="navigation" id="toc" open><summary>Table of contents</summary><ul>
<li><span class="stability_2"><a href="#assert">Assert</a></span>
<ul>
<li><a href="#strict-assertion-mode">Strict assertion mode</a></li>
<li><a href="#legacy-assertion-mode">Legacy assertion mode</a></li>
<li><a href="#class-assertassertionerror">Class: assert.AssertionError</a>
<ul>
<li><a href="#new-assertassertionerroroptions"><code>new assert.AssertionError(options)</code></a></li>
</ul>
</li>
<li><span class="stability_0"><a href="#class-assertcalltracker">Class: <code>assert.CallTracker</code></a></span>
<ul>
<li><a href="#new-assertcalltracker"><code>new assert.CallTracker()</code></a></li>
<li><a href="#trackercallsfn-exact"><code>tracker.calls([fn][, exact])</code></a></li>
<li><a href="#trackergetcallsfn"><code>tracker.getCalls(fn)</code></a></li>
<li><a href="#trackerreport"><code>tracker.report()</code></a></li>
<li><a href="#trackerresetfn"><code>tracker.reset([fn])</code></a></li>
<li><a href="#trackerverify"><code>tracker.verify()</code></a></li>
</ul>
</li>
<li><a href="#assertvalue-message"><code>assert(value[, message])</code></a></li>
<li><a href="#assertdeepequalactual-expected-message"><code>assert.deepEqual(actual, expected[, message])</code></a>
<ul>
<li><a href="#comparison-details">Comparison details</a></li>
</ul>
</li>
<li><a href="#assertdeepstrictequalactual-expected-message"><code>assert.deepStrictEqual(actual, expected[, message])</code></a>
<ul>
<li><a href="#comparison-details_1">Comparison details</a></li>
</ul>
</li>
<li><a href="#assertdoesnotmatchstring-regexp-message"><code>assert.doesNotMatch(string, regexp[, message])</code></a></li>
<li><a href="#assertdoesnotrejectasyncfn-error-message"><code>assert.doesNotReject(asyncFn[, error][, message])</code></a></li>
<li><a href="#assertdoesnotthrowfn-error-message"><code>assert.doesNotThrow(fn[, error][, message])</code></a></li>
<li><a href="#assertequalactual-expected-message"><code>assert.equal(actual, expected[, message])</code></a></li>
<li><a href="#assertfailmessage"><code>assert.fail([message])</code></a></li>
<li><span class="stability_0"><a href="#assertfailactual-expected-message-operator-stackstartfn"><code>assert.fail(actual, expected[, message[, operator[, stackStartFn]]])</code></a></span></li>
<li><a href="#assertiferrorvalue"><code>assert.ifError(value)</code></a></li>
<li><a href="#assertmatchstring-regexp-message"><code>assert.match(string, regexp[, message])</code></a></li>
<li><a href="#assertnotdeepequalactual-expected-message"><code>assert.notDeepEqual(actual, expected[, message])</code></a></li>
<li><a href="#assertnotdeepstrictequalactual-expected-message"><code>assert.notDeepStrictEqual(actual, expected[, message])</code></a></li>
<li><a href="#assertnotequalactual-expected-message"><code>assert.notEqual(actual, expected[, message])</code></a></li>
<li><a href="#assertnotstrictequalactual-expected-message"><code>assert.notStrictEqual(actual, expected[, message])</code></a></li>
<li><a href="#assertokvalue-message"><code>assert.ok(value[, message])</code></a></li>
<li><a href="#assertrejectsasyncfn-error-message"><code>assert.rejects(asyncFn[, error][, message])</code></a></li>
<li><a href="#assertstrictequalactual-expected-message"><code>assert.strictEqual(actual, expected[, message])</code></a></li>
<li><a href="#assertthrowsfn-error-message"><code>assert.throws(fn[, error][, message])</code></a></li>
</ul>
</li>
</ul></details>
<div role="main" id="apicontent">
<h2>Assert<span><a class="mark" href="#assert" id="assert">#</a></span><a aria-hidden="true" class="legacy" id="assert_assert"></a></h2>
<p></p><div class="api_stability api_stability_2"><a href="documentation.html#stability-index">Stability: 2</a> - Stable</div><p></p>
<p><strong>Source Code:</strong> <a href="https://github.com/nodejs/node/blob/v20.18.0/lib/assert.js">lib/assert.js</a></p>
<p>The <code>node:assert</code> module provides a set of assertion functions for verifying
invariants.</p>
<section><h3>Strict assertion mode<span><a class="mark" href="#strict-assertion-mode" id="strict-assertion-mode">#</a></span><a aria-hidden="true" class="legacy" id="assert_strict_assertion_mode"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v15.0.0</td>
<td><p>Exposed as <code>require('node:assert/strict')</code>.</p></td></tr>
<tr><td>v13.9.0, v12.16.2</td>
<td><p>Changed "strict mode" to "strict assertion mode" and "legacy mode" to "legacy assertion mode" to avoid confusion with the more usual meaning of "strict mode".</p></td></tr>
<tr><td>v9.9.0</td>
<td><p>Added error diffs to the strict assertion mode.</p></td></tr>
<tr><td>v9.9.0</td>
<td><p>Added strict assertion mode to the assert module.</p></td></tr>
<tr><td>v9.9.0</td>
<td><p><span>Added in: v9.9.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<p>In strict assertion mode, non-strict methods behave like their corresponding
strict methods. For example, <a href="#assertdeepequalactual-expected-message"><code>assert.deepEqual()</code></a> will behave like
<a href="#assertdeepstrictequalactual-expected-message"><code>assert.deepStrictEqual()</code></a>.</p>
<p>In strict assertion mode, error messages for objects display a diff. In legacy
assertion mode, error messages for objects display the objects, often truncated.</p>
<p>To use strict assertion mode:</p>
<pre class="with-47-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { strict <span class="hljs-keyword">as</span> assert } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>).<span class="hljs-property">strict</span>;</code><button class="copy-button">copy</button></pre>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);</code><button class="copy-button">copy</button></pre>
<p>Example error diff:</p>
<pre class="with-47-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { strict <span class="hljs-keyword">as</span> assert } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
assert.<span class="hljs-title function_">deepEqual</span>([[[<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>]], <span class="hljs-number">4</span>, <span class="hljs-number">5</span>], [[[<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-string">'3'</span>]], <span class="hljs-number">4</span>, <span class="hljs-number">5</span>]);
<span class="hljs-comment">// AssertionError: Expected inputs to be strictly deep-equal:</span>
<span class="hljs-comment">// + actual - expected ... Lines skipped</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// [</span>
<span class="hljs-comment">// [</span>
<span class="hljs-comment">// ...</span>
<span class="hljs-comment">// 2,</span>
<span class="hljs-comment">// + 3</span>
<span class="hljs-comment">// - '3'</span>
<span class="hljs-comment">// ],</span>
<span class="hljs-comment">// ...</span>
<span class="hljs-comment">// 5</span>
<span class="hljs-comment">// ]</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
assert.<span class="hljs-title function_">deepEqual</span>([[[<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>]], <span class="hljs-number">4</span>, <span class="hljs-number">5</span>], [[[<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-string">'3'</span>]], <span class="hljs-number">4</span>, <span class="hljs-number">5</span>]);
<span class="hljs-comment">// AssertionError: Expected inputs to be strictly deep-equal:</span>
<span class="hljs-comment">// + actual - expected ... Lines skipped</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// [</span>
<span class="hljs-comment">// [</span>
<span class="hljs-comment">// ...</span>
<span class="hljs-comment">// 2,</span>
<span class="hljs-comment">// + 3</span>
<span class="hljs-comment">// - '3'</span>
<span class="hljs-comment">// ],</span>
<span class="hljs-comment">// ...</span>
<span class="hljs-comment">// 5</span>
<span class="hljs-comment">// ]</span></code><button class="copy-button">copy</button></pre>
<p>To deactivate the colors, use the <code>NO_COLOR</code> or <code>NODE_DISABLE_COLORS</code>
environment variables. This will also deactivate the colors in the REPL. For
more on color support in terminal environments, read the tty
<a href="tty.html#writestreamgetcolordepthenv"><code>getColorDepth()</code></a> documentation.</p>
</section><section><h3>Legacy assertion mode<span><a class="mark" href="#legacy-assertion-mode" id="legacy-assertion-mode">#</a></span><a aria-hidden="true" class="legacy" id="assert_legacy_assertion_mode"></a></h3>
<p>Legacy assertion mode uses the <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Equality"><code>==</code> operator</a> in:</p>
<ul>
<li><a href="#assertdeepequalactual-expected-message"><code>assert.deepEqual()</code></a></li>
<li><a href="#assertequalactual-expected-message"><code>assert.equal()</code></a></li>
<li><a href="#assertnotdeepequalactual-expected-message"><code>assert.notDeepEqual()</code></a></li>
<li><a href="#assertnotequalactual-expected-message"><code>assert.notEqual()</code></a></li>
</ul>
<p>To use legacy assertion mode:</p>
<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);</code><button class="copy-button">copy</button></pre>
<p>Legacy assertion mode may have surprising results, especially when using
<a href="#assertdeepequalactual-expected-message"><code>assert.deepEqual()</code></a>:</p>
<pre><code class="language-js cjs"><span class="hljs-comment">// WARNING: This does not throw an AssertionError in legacy assertion mode!</span>
assert.<span class="hljs-title function_">deepEqual</span>(<span class="hljs-regexp">/a/gi</span>, <span class="hljs-keyword">new</span> <span class="hljs-title class_">Date</span>());</code> <button class="copy-button">copy</button></pre>
</section><section><h3>Class: assert.AssertionError<a class="srclink" href="https://github.com/nodejs/node/blob/7eebd17fa2c1e48e4534f3a69560388fab2f2c07/lib/assert.js#L143">[src]</a><span><a class="mark" href="#class-assertassertionerror" id="class-assertassertionerror">#</a></span><a aria-hidden="true" class="legacy" id="assert_class_assert_assertionerror"></a></h3>
<ul>
<li>Extends: <a href="errors.html#class-error" class="type"><errors.Error></a></li>
</ul>
<p>Indicates the failure of an assertion. All errors thrown by the <code>node:assert</code>
module will be instances of the <code>AssertionError</code> class.</p>
<h4><code>new assert.AssertionError(options)</code><span><a class="mark" href="#new-assertassertionerroroptions" id="new-assertassertionerroroptions">#</a></span><a aria-hidden="true" class="legacy" id="assert_new_assert_assertionerror_options"></a></h4>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div>
<ul>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> If provided, the error message is set to this value.</li>
<li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> The <code>actual</code> property on the error instance.</li>
<li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> The <code>expected</code> property on the error instance.</li>
<li><code>operator</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The <code>operator</code> property on the error instance.</li>
<li><code>stackStartFn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> If provided, the generated stack trace omits
frames before this function.</li>
</ul>
</li>
</ul>
<p>A subclass of <code>Error</code> that indicates the failure of an assertion.</p>
<p>All instances contain the built-in <code>Error</code> properties (<code>message</code> and <code>name</code>)
and:</p>
<ul>
<li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> Set to the <code>actual</code> argument for methods such as
<a href="#assertstrictequalactual-expected-message"><code>assert.strictEqual()</code></a>.</li>
<li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> Set to the <code>expected</code> value for methods such as
<a href="#assertstrictequalactual-expected-message"><code>assert.strictEqual()</code></a>.</li>
<li><code>generatedMessage</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> Indicates if the message was auto-generated
(<code>true</code>) or not.</li>
<li><code>code</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Value is always <code>ERR_ASSERTION</code> to show that the error is an
assertion error.</li>
<li><code>operator</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Set to the passed in operator value.</li>
</ul>
<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-comment">// Generate an AssertionError to compare the error message later:</span>
<span class="hljs-keyword">const</span> { message } = <span class="hljs-keyword">new</span> assert.<span class="hljs-title class_">AssertionError</span>({
<span class="hljs-attr">actual</span>: <span class="hljs-number">1</span>,
<span class="hljs-attr">expected</span>: <span class="hljs-number">2</span>,
<span class="hljs-attr">operator</span>: <span class="hljs-string">'strictEqual'</span>,
});
<span class="hljs-comment">// Verify error output:</span>
<span class="hljs-keyword">try</span> {
assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>);
} <span class="hljs-keyword">catch</span> (err) {
<span class="hljs-title function_">assert</span>(err <span class="hljs-keyword">instanceof</span> assert.<span class="hljs-property">AssertionError</span>);
assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">message</span>, message);
assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">name</span>, <span class="hljs-string">'AssertionError'</span>);
assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">actual</span>, <span class="hljs-number">1</span>);
assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">expected</span>, <span class="hljs-number">2</span>);
assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">code</span>, <span class="hljs-string">'ERR_ASSERTION'</span>);
assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">operator</span>, <span class="hljs-string">'strictEqual'</span>);
assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">generatedMessage</span>, <span class="hljs-literal">true</span>);
}</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-comment">// Generate an AssertionError to compare the error message later:</span>
<span class="hljs-keyword">const</span> { message } = <span class="hljs-keyword">new</span> assert.<span class="hljs-title class_">AssertionError</span>({
<span class="hljs-attr">actual</span>: <span class="hljs-number">1</span>,
<span class="hljs-attr">expected</span>: <span class="hljs-number">2</span>,
<span class="hljs-attr">operator</span>: <span class="hljs-string">'strictEqual'</span>,
});
<span class="hljs-comment">// Verify error output:</span>
<span class="hljs-keyword">try</span> {
assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>);
} <span class="hljs-keyword">catch</span> (err) {
<span class="hljs-title function_">assert</span>(err <span class="hljs-keyword">instanceof</span> assert.<span class="hljs-property">AssertionError</span>);
assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">message</span>, message);
assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">name</span>, <span class="hljs-string">'AssertionError'</span>);
assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">actual</span>, <span class="hljs-number">1</span>);
assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">expected</span>, <span class="hljs-number">2</span>);
assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">code</span>, <span class="hljs-string">'ERR_ASSERTION'</span>);
assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">operator</span>, <span class="hljs-string">'strictEqual'</span>);
assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">generatedMessage</span>, <span class="hljs-literal">true</span>);
}</code><button class="copy-button">copy</button></pre>
</section><section><h3>Class: <code>assert.CallTracker</code><span><a class="mark" href="#class-assertcalltracker" id="class-assertcalltracker">#</a></span><a aria-hidden="true" class="legacy" id="assert_class_assert_calltracker"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v20.1.0</td>
<td><p>the <code>assert.CallTracker</code> class has been deprecated and will be removed in a future version.</p></td></tr>
<tr><td>v14.2.0, v12.19.0</td>
<td><p><span>Added in: v14.2.0, v12.19.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated</div><p></p>
<p>This feature is deprecated and will be removed in a future version.
Please consider using alternatives such as the
<a href="test.html#mocking"><code>mock</code></a> helper function.</p>
<h4><code>new assert.CallTracker()</code><span><a class="mark" href="#new-assertcalltracker" id="new-assertcalltracker">#</a></span><a aria-hidden="true" class="legacy" id="assert_new_assert_calltracker"></a></h4>
<div class="api_metadata">
<span>Added in: v14.2.0, v12.19.0</span>
</div>
<p>Creates a new <a href="#class-assertcalltracker"><code>CallTracker</code></a> object which can be used to track if functions
were called a specific number of times. The <code>tracker.verify()</code> must be called
for the verification to take place. The usual pattern would be to call it in a
<a href="process.html#event-exit"><code>process.on('exit')</code></a> handler.</p>
<pre class="with-40-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-keyword">import</span> process <span class="hljs-keyword">from</span> <span class="hljs-string">'node:process'</span>;
<span class="hljs-keyword">const</span> tracker = <span class="hljs-keyword">new</span> assert.<span class="hljs-title class_">CallTracker</span>();
<span class="hljs-keyword">function</span> <span class="hljs-title function_">func</span>(<span class="hljs-params"></span>) {}
<span class="hljs-comment">// callsfunc() must be called exactly 1 time before tracker.verify().</span>
<span class="hljs-keyword">const</span> callsfunc = tracker.<span class="hljs-title function_">calls</span>(func, <span class="hljs-number">1</span>);
<span class="hljs-title function_">callsfunc</span>();
<span class="hljs-comment">// Calls tracker.verify() and verifies if all tracker.calls() functions have</span>
<span class="hljs-comment">// been called exact times.</span>
process.<span class="hljs-title function_">on</span>(<span class="hljs-string">'exit'</span>, <span class="hljs-function">() =></span> {
tracker.<span class="hljs-title function_">verify</span>();
});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> process = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:process'</span>);
<span class="hljs-keyword">const</span> tracker = <span class="hljs-keyword">new</span> assert.<span class="hljs-title class_">CallTracker</span>();
<span class="hljs-keyword">function</span> <span class="hljs-title function_">func</span>(<span class="hljs-params"></span>) {}
<span class="hljs-comment">// callsfunc() must be called exactly 1 time before tracker.verify().</span>
<span class="hljs-keyword">const</span> callsfunc = tracker.<span class="hljs-title function_">calls</span>(func, <span class="hljs-number">1</span>);
<span class="hljs-title function_">callsfunc</span>();
<span class="hljs-comment">// Calls tracker.verify() and verifies if all tracker.calls() functions have</span>
<span class="hljs-comment">// been called exact times.</span>
process.<span class="hljs-title function_">on</span>(<span class="hljs-string">'exit'</span>, <span class="hljs-function">() =></span> {
tracker.<span class="hljs-title function_">verify</span>();
});</code><button class="copy-button">copy</button></pre>
<h4><code>tracker.calls([fn][, exact])</code><span><a class="mark" href="#trackercallsfn-exact" id="trackercallsfn-exact">#</a></span><a aria-hidden="true" class="legacy" id="assert_tracker_calls_fn_exact"></a></h4>
<div class="api_metadata">
<span>Added in: v14.2.0, v12.19.0</span>
</div>
<ul>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> <strong>Default:</strong> A no-op function.</li>
<li><code>exact</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> <strong>Default:</strong> <code>1</code>.</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> A function that wraps <code>fn</code>.</li>
</ul>
<p>The wrapper function is expected to be called exactly <code>exact</code> times. If the
function has not been called exactly <code>exact</code> times when
<a href="#trackerverify"><code>tracker.verify()</code></a> is called, then <a href="#trackerverify"><code>tracker.verify()</code></a> will throw an
error.</p>
<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-comment">// Creates call tracker.</span>
<span class="hljs-keyword">const</span> tracker = <span class="hljs-keyword">new</span> assert.<span class="hljs-title class_">CallTracker</span>();
<span class="hljs-keyword">function</span> <span class="hljs-title function_">func</span>(<span class="hljs-params"></span>) {}
<span class="hljs-comment">// Returns a function that wraps func() that must be called exact times</span>
<span class="hljs-comment">// before tracker.verify().</span>
<span class="hljs-keyword">const</span> callsfunc = tracker.<span class="hljs-title function_">calls</span>(func);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-comment">// Creates call tracker.</span>
<span class="hljs-keyword">const</span> tracker = <span class="hljs-keyword">new</span> assert.<span class="hljs-title class_">CallTracker</span>();
<span class="hljs-keyword">function</span> <span class="hljs-title function_">func</span>(<span class="hljs-params"></span>) {}
<span class="hljs-comment">// Returns a function that wraps func() that must be called exact times</span>
<span class="hljs-comment">// before tracker.verify().</span>
<span class="hljs-keyword">const</span> callsfunc = tracker.<span class="hljs-title function_">calls</span>(func);</code><button class="copy-button">copy</button></pre>
<h4><code>tracker.getCalls(fn)</code><span><a class="mark" href="#trackergetcallsfn" id="trackergetcallsfn">#</a></span><a aria-hidden="true" class="legacy" id="assert_tracker_getcalls_fn"></a></h4>
<div class="api_metadata">
<span>Added in: v18.8.0, v16.18.0</span>
</div>
<ul>
<li>
<p><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></p>
</li>
<li>
<p>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> An array with all the calls to a tracked function.</p>
</li>
<li>
<p>Object <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></p>
<ul>
<li><code>thisArg</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
<li><code>arguments</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> the arguments passed to the tracked function</li>
</ul>
</li>
</ul>
<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-keyword">const</span> tracker = <span class="hljs-keyword">new</span> assert.<span class="hljs-title class_">CallTracker</span>();
<span class="hljs-keyword">function</span> <span class="hljs-title function_">func</span>(<span class="hljs-params"></span>) {}
<span class="hljs-keyword">const</span> callsfunc = tracker.<span class="hljs-title function_">calls</span>(func);
<span class="hljs-title function_">callsfunc</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>);
assert.<span class="hljs-title function_">deepStrictEqual</span>(tracker.<span class="hljs-title function_">getCalls</span>(callsfunc),
[{ <span class="hljs-attr">thisArg</span>: <span class="hljs-literal">undefined</span>, <span class="hljs-attr">arguments</span>: [<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>] }]);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-comment">// Creates call tracker.</span>
<span class="hljs-keyword">const</span> tracker = <span class="hljs-keyword">new</span> assert.<span class="hljs-title class_">CallTracker</span>();
<span class="hljs-keyword">function</span> <span class="hljs-title function_">func</span>(<span class="hljs-params"></span>) {}
<span class="hljs-keyword">const</span> callsfunc = tracker.<span class="hljs-title function_">calls</span>(func);
<span class="hljs-title function_">callsfunc</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>);
assert.<span class="hljs-title function_">deepStrictEqual</span>(tracker.<span class="hljs-title function_">getCalls</span>(callsfunc),
[{ <span class="hljs-attr">thisArg</span>: <span class="hljs-literal">undefined</span>, <span class="hljs-attr">arguments</span>: [<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>] }]);</code><button class="copy-button">copy</button></pre>
<h4><code>tracker.report()</code><span><a class="mark" href="#trackerreport" id="trackerreport">#</a></span><a aria-hidden="true" class="legacy" id="assert_tracker_report"></a></h4>
<div class="api_metadata">
<span>Added in: v14.2.0, v12.19.0</span>
</div>
<ul>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> An array of objects containing information about the wrapper
functions returned by <a href="#trackercallsfn-exact"><code>tracker.calls()</code></a>.</li>
<li>Object <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
<li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The actual number of times the function was called.</li>
<li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The number of times the function was expected to be
called.</li>
<li><code>operator</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The name of the function that is wrapped.</li>
<li><code>stack</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> A stack trace of the function.</li>
</ul>
</li>
</ul>
<p>The arrays contains information about the expected and actual number of calls of
the functions that have not been called the expected number of times.</p>
<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-comment">// Creates call tracker.</span>
<span class="hljs-keyword">const</span> tracker = <span class="hljs-keyword">new</span> assert.<span class="hljs-title class_">CallTracker</span>();
<span class="hljs-keyword">function</span> <span class="hljs-title function_">func</span>(<span class="hljs-params"></span>) {}
<span class="hljs-comment">// Returns a function that wraps func() that must be called exact times</span>
<span class="hljs-comment">// before tracker.verify().</span>
<span class="hljs-keyword">const</span> callsfunc = tracker.<span class="hljs-title function_">calls</span>(func, <span class="hljs-number">2</span>);
<span class="hljs-comment">// Returns an array containing information on callsfunc()</span>
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(tracker.<span class="hljs-title function_">report</span>());
<span class="hljs-comment">// [</span>
<span class="hljs-comment">// {</span>
<span class="hljs-comment">// message: 'Expected the func function to be executed 2 time(s) but was</span>
<span class="hljs-comment">// executed 0 time(s).',</span>
<span class="hljs-comment">// actual: 0,</span>
<span class="hljs-comment">// expected: 2,</span>
<span class="hljs-comment">// operator: 'func',</span>
<span class="hljs-comment">// stack: stack trace</span>
<span class="hljs-comment">// }</span>
<span class="hljs-comment">// ]</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-comment">// Creates call tracker.</span>
<span class="hljs-keyword">const</span> tracker = <span class="hljs-keyword">new</span> assert.<span class="hljs-title class_">CallTracker</span>();
<span class="hljs-keyword">function</span> <span class="hljs-title function_">func</span>(<span class="hljs-params"></span>) {}
<span class="hljs-comment">// Returns a function that wraps func() that must be called exact times</span>
<span class="hljs-comment">// before tracker.verify().</span>
<span class="hljs-keyword">const</span> callsfunc = tracker.<span class="hljs-title function_">calls</span>(func, <span class="hljs-number">2</span>);
<span class="hljs-comment">// Returns an array containing information on callsfunc()</span>
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(tracker.<span class="hljs-title function_">report</span>());
<span class="hljs-comment">// [</span>
<span class="hljs-comment">// {</span>
<span class="hljs-comment">// message: 'Expected the func function to be executed 2 time(s) but was</span>
<span class="hljs-comment">// executed 0 time(s).',</span>
<span class="hljs-comment">// actual: 0,</span>
<span class="hljs-comment">// expected: 2,</span>
<span class="hljs-comment">// operator: 'func',</span>
<span class="hljs-comment">// stack: stack trace</span>
<span class="hljs-comment">// }</span>
<span class="hljs-comment">// ]</span></code><button class="copy-button">copy</button></pre>
<h4><code>tracker.reset([fn])</code><span><a class="mark" href="#trackerresetfn" id="trackerresetfn">#</a></span><a aria-hidden="true" class="legacy" id="assert_tracker_reset_fn"></a></h4>
<div class="api_metadata">
<span>Added in: v18.8.0, v16.18.0</span>
</div>
<ul>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> a tracked function to reset.</li>
</ul>
<p>Reset calls of the call tracker.
If a tracked function is passed as an argument, the calls will be reset for it.
If no arguments are passed, all tracked functions will be reset.</p>
<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-keyword">const</span> tracker = <span class="hljs-keyword">new</span> assert.<span class="hljs-title class_">CallTracker</span>();
<span class="hljs-keyword">function</span> <span class="hljs-title function_">func</span>(<span class="hljs-params"></span>) {}
<span class="hljs-keyword">const</span> callsfunc = tracker.<span class="hljs-title function_">calls</span>(func);
<span class="hljs-title function_">callsfunc</span>();
<span class="hljs-comment">// Tracker was called once</span>
assert.<span class="hljs-title function_">strictEqual</span>(tracker.<span class="hljs-title function_">getCalls</span>(callsfunc).<span class="hljs-property">length</span>, <span class="hljs-number">1</span>);
tracker.<span class="hljs-title function_">reset</span>(callsfunc);
assert.<span class="hljs-title function_">strictEqual</span>(tracker.<span class="hljs-title function_">getCalls</span>(callsfunc).<span class="hljs-property">length</span>, <span class="hljs-number">0</span>);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> tracker = <span class="hljs-keyword">new</span> assert.<span class="hljs-title class_">CallTracker</span>();
<span class="hljs-keyword">function</span> <span class="hljs-title function_">func</span>(<span class="hljs-params"></span>) {}
<span class="hljs-keyword">const</span> callsfunc = tracker.<span class="hljs-title function_">calls</span>(func);
<span class="hljs-title function_">callsfunc</span>();
<span class="hljs-comment">// Tracker was called once</span>
assert.<span class="hljs-title function_">strictEqual</span>(tracker.<span class="hljs-title function_">getCalls</span>(callsfunc).<span class="hljs-property">length</span>, <span class="hljs-number">1</span>);
tracker.<span class="hljs-title function_">reset</span>(callsfunc);
assert.<span class="hljs-title function_">strictEqual</span>(tracker.<span class="hljs-title function_">getCalls</span>(callsfunc).<span class="hljs-property">length</span>, <span class="hljs-number">0</span>);</code><button class="copy-button">copy</button></pre>
<h4><code>tracker.verify()</code><span><a class="mark" href="#trackerverify" id="trackerverify">#</a></span><a aria-hidden="true" class="legacy" id="assert_tracker_verify"></a></h4>
<div class="api_metadata">
<span>Added in: v14.2.0, v12.19.0</span>
</div>
<p>Iterates through the list of functions passed to
<a href="#trackercallsfn-exact"><code>tracker.calls()</code></a> and will throw an error for functions that
have not been called the expected number of times.</p>
<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-comment">// Creates call tracker.</span>
<span class="hljs-keyword">const</span> tracker = <span class="hljs-keyword">new</span> assert.<span class="hljs-title class_">CallTracker</span>();
<span class="hljs-keyword">function</span> <span class="hljs-title function_">func</span>(<span class="hljs-params"></span>) {}
<span class="hljs-comment">// Returns a function that wraps func() that must be called exact times</span>
<span class="hljs-comment">// before tracker.verify().</span>
<span class="hljs-keyword">const</span> callsfunc = tracker.<span class="hljs-title function_">calls</span>(func, <span class="hljs-number">2</span>);
<span class="hljs-title function_">callsfunc</span>();
<span class="hljs-comment">// Will throw an error since callsfunc() was only called once.</span>
tracker.<span class="hljs-title function_">verify</span>();</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-comment">// Creates call tracker.</span>
<span class="hljs-keyword">const</span> tracker = <span class="hljs-keyword">new</span> assert.<span class="hljs-title class_">CallTracker</span>();
<span class="hljs-keyword">function</span> <span class="hljs-title function_">func</span>(<span class="hljs-params"></span>) {}
<span class="hljs-comment">// Returns a function that wraps func() that must be called exact times</span>
<span class="hljs-comment">// before tracker.verify().</span>
<span class="hljs-keyword">const</span> callsfunc = tracker.<span class="hljs-title function_">calls</span>(func, <span class="hljs-number">2</span>);
<span class="hljs-title function_">callsfunc</span>();
<span class="hljs-comment">// Will throw an error since callsfunc() was only called once.</span>
tracker.<span class="hljs-title function_">verify</span>();</code><button class="copy-button">copy</button></pre>
</section><section><h3><code>assert(value[, message])</code><span><a class="mark" href="#assertvalue-message" id="assertvalue-message">#</a></span><a aria-hidden="true" class="legacy" id="assert_assert_value_message"></a></h3>
<div class="api_metadata">
<span>Added in: v0.5.9</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> The input that is checked for being truthy.</li>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li>
</ul>
<p>An alias of <a href="#assertokvalue-message"><code>assert.ok()</code></a>.</p>
</section><section><h3><code>assert.deepEqual(actual, expected[, message])</code><span><a class="mark" href="#assertdeepequalactual-expected-message" id="assertdeepequalactual-expected-message">#</a></span><a aria-hidden="true" class="legacy" id="assert_assert_deepequal_actual_expected_message"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v20.15.0</td>
<td><p>Error cause and errors properties are now compared as well.</p></td></tr>
<tr><td>v18.0.0</td>
<td><p>Regular expressions lastIndex property is now compared as well.</p></td></tr>
<tr><td>v16.0.0, v14.18.0</td>
<td><p>In Legacy assertion mode, changed status from Deprecated to Legacy.</p></td></tr>
<tr><td>v14.0.0</td>
<td><p>NaN is now treated as being identical if both sides are NaN.</p></td></tr>
<tr><td>v12.0.0</td>
<td><p>The type tags are now properly compared and there are a couple minor comparison adjustments to make the check less surprising.</p></td></tr>
<tr><td>v9.0.0</td>
<td><p>The <code>Error</code> names and messages are now properly compared.</p></td></tr>
<tr><td>v8.0.0</td>
<td><p>The <code>Set</code> and <code>Map</code> content is also compared.</p></td></tr>
<tr><td>v6.4.0, v4.7.1</td>
<td><p>Typed array slices are handled correctly now.</p></td></tr>
<tr><td>v6.1.0, v4.5.0</td>
<td><p>Objects with circular references can be used as inputs now.</p></td></tr>
<tr><td>v5.10.1, v4.4.3</td>
<td><p>Handle non-<code>Uint8Array</code> typed arrays correctly.</p></td></tr>
<tr><td>v0.1.21</td>
<td><p><span>Added in: v0.1.21</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li>
</ul>
<p><strong>Strict assertion mode</strong></p>
<p>An alias of <a href="#assertdeepstrictequalactual-expected-message"><code>assert.deepStrictEqual()</code></a>.</p>
<p><strong>Legacy assertion mode</strong></p>
<p></p><div class="api_stability api_stability_3"><a href="documentation.html#stability-index">Stability: 3</a> - Legacy: Use <a href="#assertdeepstrictequalactual-expected-message"><code>assert.deepStrictEqual()</code></a> instead.</div><p></p>
<p>Tests for deep equality between the <code>actual</code> and <code>expected</code> parameters. Consider
using <a href="#assertdeepstrictequalactual-expected-message"><code>assert.deepStrictEqual()</code></a> instead. <a href="#assertdeepequalactual-expected-message"><code>assert.deepEqual()</code></a> can have
surprising results.</p>
<p><em>Deep equality</em> means that the enumerable "own" properties of child objects
are also recursively evaluated by the following rules.</p>
<h4>Comparison details<span><a class="mark" href="#comparison-details" id="comparison-details">#</a></span><a aria-hidden="true" class="legacy" id="assert_comparison_details"></a></h4>
<ul>
<li>Primitive values are compared with the <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Equality"><code>==</code> operator</a>,
with the exception of <code>NaN</code>. It is treated as being identical in case
both sides are <code>NaN</code>.</li>
<li><a href="https://tc39.github.io/ecma262/#sec-object.prototype.tostring">Type tags</a> of objects should be the same.</li>
<li>Only <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties">enumerable "own" properties</a> are considered.</li>
<li><a href="errors.html#class-error"><code>Error</code></a> names, messages, causes, and errors are always compared,
even if these are not enumerable properties.</li>
<li><a href="https://developer.mozilla.org/en-US/docs/Glossary/Primitive#Primitive_wrapper_objects_in_JavaScript">Object wrappers</a> are compared both as objects and unwrapped values.</li>
<li><code>Object</code> properties are compared unordered.</li>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map"><code>Map</code></a> keys and <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set"><code>Set</code></a> items are compared unordered.</li>
<li>Recursion stops when both sides differ or both sides encounter a circular
reference.</li>
<li>Implementation does not test the <a href="https://tc39.github.io/ecma262/#sec-ordinary-object-internal-methods-and-internal-slots"><code>[[Prototype]]</code></a> of
objects.</li>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol"><code>Symbol</code></a> properties are not compared.</li>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap"><code>WeakMap</code></a> and <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet"><code>WeakSet</code></a> comparison does not rely on their values.</li>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a> lastIndex, flags, and source are always compared, even if these
are not enumerable properties.</li>
</ul>
<p>The following example does not throw an <a href="#class-assertassertionerror"><code>AssertionError</code></a> because the
primitives are compared using the <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Equality"><code>==</code> operator</a>.</p>
<pre class="with-50-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-comment">// WARNING: This does not throw an AssertionError!</span>
assert.<span class="hljs-title function_">deepEqual</span>(<span class="hljs-string">'+00000000'</span>, <span class="hljs-literal">false</span>);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-comment">// WARNING: This does not throw an AssertionError!</span>
assert.<span class="hljs-title function_">deepEqual</span>(<span class="hljs-string">'+00000000'</span>, <span class="hljs-literal">false</span>);</code><button class="copy-button">copy</button></pre>
<p>"Deep" equality means that the enumerable "own" properties of child objects
are evaluated also:</p>
<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-keyword">const</span> obj1 = {
<span class="hljs-attr">a</span>: {
<span class="hljs-attr">b</span>: <span class="hljs-number">1</span>,
},
};
<span class="hljs-keyword">const</span> obj2 = {
<span class="hljs-attr">a</span>: {
<span class="hljs-attr">b</span>: <span class="hljs-number">2</span>,
},
};
<span class="hljs-keyword">const</span> obj3 = {
<span class="hljs-attr">a</span>: {
<span class="hljs-attr">b</span>: <span class="hljs-number">1</span>,
},
};
<span class="hljs-keyword">const</span> obj4 = { <span class="hljs-attr">__proto__</span>: obj1 };
assert.<span class="hljs-title function_">deepEqual</span>(obj1, obj1);
<span class="hljs-comment">// OK</span>
<span class="hljs-comment">// Values of b are different:</span>
assert.<span class="hljs-title function_">deepEqual</span>(obj1, obj2);
<span class="hljs-comment">// AssertionError: { a: { b: 1 } } deepEqual { a: { b: 2 } }</span>
assert.<span class="hljs-title function_">deepEqual</span>(obj1, obj3);
<span class="hljs-comment">// OK</span>
<span class="hljs-comment">// Prototypes are ignored:</span>
assert.<span class="hljs-title function_">deepEqual</span>(obj1, obj4);
<span class="hljs-comment">// AssertionError: { a: { b: 1 } } deepEqual {}</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> obj1 = {
<span class="hljs-attr">a</span>: {
<span class="hljs-attr">b</span>: <span class="hljs-number">1</span>,
},
};
<span class="hljs-keyword">const</span> obj2 = {
<span class="hljs-attr">a</span>: {
<span class="hljs-attr">b</span>: <span class="hljs-number">2</span>,
},
};
<span class="hljs-keyword">const</span> obj3 = {
<span class="hljs-attr">a</span>: {
<span class="hljs-attr">b</span>: <span class="hljs-number">1</span>,
},
};
<span class="hljs-keyword">const</span> obj4 = { <span class="hljs-attr">__proto__</span>: obj1 };
assert.<span class="hljs-title function_">deepEqual</span>(obj1, obj1);
<span class="hljs-comment">// OK</span>
<span class="hljs-comment">// Values of b are different:</span>
assert.<span class="hljs-title function_">deepEqual</span>(obj1, obj2);
<span class="hljs-comment">// AssertionError: { a: { b: 1 } } deepEqual { a: { b: 2 } }</span>
assert.<span class="hljs-title function_">deepEqual</span>(obj1, obj3);
<span class="hljs-comment">// OK</span>
<span class="hljs-comment">// Prototypes are ignored:</span>
assert.<span class="hljs-title function_">deepEqual</span>(obj1, obj4);
<span class="hljs-comment">// AssertionError: { a: { b: 1 } } deepEqual {}</span></code><button class="copy-button">copy</button></pre>
<p>If the values are not equal, an <a href="#class-assertassertionerror"><code>AssertionError</code></a> is thrown with a <code>message</code>
property set equal to the value of the <code>message</code> parameter. If the <code>message</code>
parameter is undefined, a default error message is assigned. If the <code>message</code>
parameter is an instance of an <a href="errors.html#class-error"><code>Error</code></a> then it will be thrown instead of the
<a href="#class-assertassertionerror"><code>AssertionError</code></a>.</p>
</section><section><h3><code>assert.deepStrictEqual(actual, expected[, message])</code><span><a class="mark" href="#assertdeepstrictequalactual-expected-message" id="assertdeepstrictequalactual-expected-message">#</a></span><a aria-hidden="true" class="legacy" id="assert_assert_deepstrictequal_actual_expected_message"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v20.15.0</td>
<td><p>Error cause and errors properties are now compared as well.</p></td></tr>
<tr><td>v18.0.0</td>
<td><p>Regular expressions lastIndex property is now compared as well.</p></td></tr>
<tr><td>v9.0.0</td>
<td><p>Enumerable symbol properties are now compared.</p></td></tr>
<tr><td>v9.0.0</td>
<td><p>The <code>NaN</code> is now compared using the <a href="https://tc39.github.io/ecma262/#sec-samevaluezero">SameValueZero</a> comparison.</p></td></tr>
<tr><td>v8.5.0</td>
<td><p>The <code>Error</code> names and messages are now properly compared.</p></td></tr>
<tr><td>v8.0.0</td>
<td><p>The <code>Set</code> and <code>Map</code> content is also compared.</p></td></tr>
<tr><td>v6.1.0</td>
<td><p>Objects with circular references can be used as inputs now.</p></td></tr>
<tr><td>v6.4.0, v4.7.1</td>
<td><p>Typed array slices are handled correctly now.</p></td></tr>
<tr><td>v5.10.1, v4.4.3</td>
<td><p>Handle non-<code>Uint8Array</code> typed arrays correctly.</p></td></tr>
<tr><td>v1.2.0</td>
<td><p><span>Added in: v1.2.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li>
</ul>
<p>Tests for deep equality between the <code>actual</code> and <code>expected</code> parameters.
"Deep" equality means that the enumerable "own" properties of child objects
are recursively evaluated also by the following rules.</p>
<h4>Comparison details<span><a class="mark" href="#comparison-details_1" id="comparison-details_1">#</a></span><a aria-hidden="true" class="legacy" id="assert_comparison_details_1"></a></h4>
<ul>
<li>Primitive values are compared using <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is"><code>Object.is()</code></a>.</li>
<li><a href="https://tc39.github.io/ecma262/#sec-object.prototype.tostring">Type tags</a> of objects should be the same.</li>
<li><a href="https://tc39.github.io/ecma262/#sec-ordinary-object-internal-methods-and-internal-slots"><code>[[Prototype]]</code></a> of objects are compared using
the <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Strict_equality"><code>===</code> operator</a>.</li>
<li>Only <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties">enumerable "own" properties</a> are considered.</li>
<li><a href="errors.html#class-error"><code>Error</code></a> names, messages, causes, and errors are always compared,
even if these are not enumerable properties.
<code>errors</code> is also compared.</li>
<li>Enumerable own <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol"><code>Symbol</code></a> properties are compared as well.</li>
<li><a href="https://developer.mozilla.org/en-US/docs/Glossary/Primitive#Primitive_wrapper_objects_in_JavaScript">Object wrappers</a> are compared both as objects and unwrapped values.</li>
<li><code>Object</code> properties are compared unordered.</li>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map"><code>Map</code></a> keys and <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set"><code>Set</code></a> items are compared unordered.</li>
<li>Recursion stops when both sides differ or both sides encounter a circular
reference.</li>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap"><code>WeakMap</code></a> and <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet"><code>WeakSet</code></a> comparison does not rely on their values. See
below for further details.</li>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a> lastIndex, flags, and source are always compared, even if these
are not enumerable properties.</li>
</ul>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
<span class="hljs-comment">// This fails because 1 !== '1'.</span>
assert.<span class="hljs-title function_">deepStrictEqual</span>({ <span class="hljs-attr">a</span>: <span class="hljs-number">1</span> }, { <span class="hljs-attr">a</span>: <span class="hljs-string">'1'</span> });
<span class="hljs-comment">// AssertionError: Expected inputs to be strictly deep-equal:</span>
<span class="hljs-comment">// + actual - expected</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// {</span>
<span class="hljs-comment">// + a: 1</span>
<span class="hljs-comment">// - a: '1'</span>
<span class="hljs-comment">// }</span>
<span class="hljs-comment">// The following objects don't have own properties</span>
<span class="hljs-keyword">const</span> date = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Date</span>();
<span class="hljs-keyword">const</span> object = {};
<span class="hljs-keyword">const</span> fakeDate = {};
<span class="hljs-title class_">Object</span>.<span class="hljs-title function_">setPrototypeOf</span>(fakeDate, <span class="hljs-title class_">Date</span>.<span class="hljs-property"><span class="hljs-keyword">prototype</span></span>);
<span class="hljs-comment">// Different [[Prototype]]:</span>
assert.<span class="hljs-title function_">deepStrictEqual</span>(object, fakeDate);
<span class="hljs-comment">// AssertionError: Expected inputs to be strictly deep-equal:</span>
<span class="hljs-comment">// + actual - expected</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// + {}</span>
<span class="hljs-comment">// - Date {}</span>
<span class="hljs-comment">// Different type tags:</span>
assert.<span class="hljs-title function_">deepStrictEqual</span>(date, fakeDate);
<span class="hljs-comment">// AssertionError: Expected inputs to be strictly deep-equal:</span>
<span class="hljs-comment">// + actual - expected</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// + 2018-04-26T00:49:08.604Z</span>
<span class="hljs-comment">// - Date {}</span>
assert.<span class="hljs-title function_">deepStrictEqual</span>(<span class="hljs-title class_">NaN</span>, <span class="hljs-title class_">NaN</span>);
<span class="hljs-comment">// OK because Object.is(NaN, NaN) is true.</span>
<span class="hljs-comment">// Different unwrapped numbers:</span>
assert.<span class="hljs-title function_">deepStrictEqual</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Number</span>(<span class="hljs-number">1</span>), <span class="hljs-keyword">new</span> <span class="hljs-title class_">Number</span>(<span class="hljs-number">2</span>));
<span class="hljs-comment">// AssertionError: Expected inputs to be strictly deep-equal:</span>
<span class="hljs-comment">// + actual - expected</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// + [Number: 1]</span>
<span class="hljs-comment">// - [Number: 2]</span>
assert.<span class="hljs-title function_">deepStrictEqual</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">String</span>(<span class="hljs-string">'foo'</span>), <span class="hljs-title class_">Object</span>(<span class="hljs-string">'foo'</span>));
<span class="hljs-comment">// OK because the object and the string are identical when unwrapped.</span>
assert.<span class="hljs-title function_">deepStrictEqual</span>(-<span class="hljs-number">0</span>, -<span class="hljs-number">0</span>);
<span class="hljs-comment">// OK</span>
<span class="hljs-comment">// Different zeros:</span>
assert.<span class="hljs-title function_">deepStrictEqual</span>(<span class="hljs-number">0</span>, -<span class="hljs-number">0</span>);
<span class="hljs-comment">// AssertionError: Expected inputs to be strictly deep-equal:</span>
<span class="hljs-comment">// + actual - expected</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// + 0</span>
<span class="hljs-comment">// - -0</span>
<span class="hljs-keyword">const</span> symbol1 = <span class="hljs-title class_">Symbol</span>();
<span class="hljs-keyword">const</span> symbol2 = <span class="hljs-title class_">Symbol</span>();
assert.<span class="hljs-title function_">deepStrictEqual</span>({ [symbol1]: <span class="hljs-number">1</span> }, { [symbol1]: <span class="hljs-number">1</span> });
<span class="hljs-comment">// OK, because it is the same symbol on both objects.</span>
assert.<span class="hljs-title function_">deepStrictEqual</span>({ [symbol1]: <span class="hljs-number">1</span> }, { [symbol2]: <span class="hljs-number">1</span> });
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: Inputs identical but not reference equal:</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// {</span>
<span class="hljs-comment">// [Symbol()]: 1</span>
<span class="hljs-comment">// }</span>
<span class="hljs-keyword">const</span> weakMap1 = <span class="hljs-keyword">new</span> <span class="hljs-title class_">WeakMap</span>();
<span class="hljs-keyword">const</span> weakMap2 = <span class="hljs-keyword">new</span> <span class="hljs-title class_">WeakMap</span>([[{}, {}]]);
<span class="hljs-keyword">const</span> weakMap3 = <span class="hljs-keyword">new</span> <span class="hljs-title class_">WeakMap</span>();
weakMap3.<span class="hljs-property">unequal</span> = <span class="hljs-literal">true</span>;
assert.<span class="hljs-title function_">deepStrictEqual</span>(weakMap1, weakMap2);
<span class="hljs-comment">// OK, because it is impossible to compare the entries</span>
<span class="hljs-comment">// Fails because weakMap3 has a property that weakMap1 does not contain:</span>
assert.<span class="hljs-title function_">deepStrictEqual</span>(weakMap1, weakMap3);
<span class="hljs-comment">// AssertionError: Expected inputs to be strictly deep-equal:</span>
<span class="hljs-comment">// + actual - expected</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// WeakMap {</span>
<span class="hljs-comment">// + [items unknown]</span>
<span class="hljs-comment">// - [items unknown],</span>
<span class="hljs-comment">// - unequal: true</span>
<span class="hljs-comment">// }</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
<span class="hljs-comment">// This fails because 1 !== '1'.</span>
assert.<span class="hljs-title function_">deepStrictEqual</span>({ <span class="hljs-attr">a</span>: <span class="hljs-number">1</span> }, { <span class="hljs-attr">a</span>: <span class="hljs-string">'1'</span> });
<span class="hljs-comment">// AssertionError: Expected inputs to be strictly deep-equal:</span>
<span class="hljs-comment">// + actual - expected</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// {</span>
<span class="hljs-comment">// + a: 1</span>
<span class="hljs-comment">// - a: '1'</span>
<span class="hljs-comment">// }</span>
<span class="hljs-comment">// The following objects don't have own properties</span>
<span class="hljs-keyword">const</span> date = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Date</span>();
<span class="hljs-keyword">const</span> object = {};
<span class="hljs-keyword">const</span> fakeDate = {};
<span class="hljs-title class_">Object</span>.<span class="hljs-title function_">setPrototypeOf</span>(fakeDate, <span class="hljs-title class_">Date</span>.<span class="hljs-property"><span class="hljs-keyword">prototype</span></span>);
<span class="hljs-comment">// Different [[Prototype]]:</span>
assert.<span class="hljs-title function_">deepStrictEqual</span>(object, fakeDate);
<span class="hljs-comment">// AssertionError: Expected inputs to be strictly deep-equal:</span>
<span class="hljs-comment">// + actual - expected</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// + {}</span>
<span class="hljs-comment">// - Date {}</span>
<span class="hljs-comment">// Different type tags:</span>
assert.<span class="hljs-title function_">deepStrictEqual</span>(date, fakeDate);
<span class="hljs-comment">// AssertionError: Expected inputs to be strictly deep-equal:</span>
<span class="hljs-comment">// + actual - expected</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// + 2018-04-26T00:49:08.604Z</span>
<span class="hljs-comment">// - Date {}</span>
assert.<span class="hljs-title function_">deepStrictEqual</span>(<span class="hljs-title class_">NaN</span>, <span class="hljs-title class_">NaN</span>);
<span class="hljs-comment">// OK because Object.is(NaN, NaN) is true.</span>
<span class="hljs-comment">// Different unwrapped numbers:</span>
assert.<span class="hljs-title function_">deepStrictEqual</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Number</span>(<span class="hljs-number">1</span>), <span class="hljs-keyword">new</span> <span class="hljs-title class_">Number</span>(<span class="hljs-number">2</span>));
<span class="hljs-comment">// AssertionError: Expected inputs to be strictly deep-equal:</span>
<span class="hljs-comment">// + actual - expected</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// + [Number: 1]</span>
<span class="hljs-comment">// - [Number: 2]</span>
assert.<span class="hljs-title function_">deepStrictEqual</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">String</span>(<span class="hljs-string">'foo'</span>), <span class="hljs-title class_">Object</span>(<span class="hljs-string">'foo'</span>));
<span class="hljs-comment">// OK because the object and the string are identical when unwrapped.</span>
assert.<span class="hljs-title function_">deepStrictEqual</span>(-<span class="hljs-number">0</span>, -<span class="hljs-number">0</span>);
<span class="hljs-comment">// OK</span>
<span class="hljs-comment">// Different zeros:</span>
assert.<span class="hljs-title function_">deepStrictEqual</span>(<span class="hljs-number">0</span>, -<span class="hljs-number">0</span>);
<span class="hljs-comment">// AssertionError: Expected inputs to be strictly deep-equal:</span>
<span class="hljs-comment">// + actual - expected</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// + 0</span>
<span class="hljs-comment">// - -0</span>
<span class="hljs-keyword">const</span> symbol1 = <span class="hljs-title class_">Symbol</span>();
<span class="hljs-keyword">const</span> symbol2 = <span class="hljs-title class_">Symbol</span>();
assert.<span class="hljs-title function_">deepStrictEqual</span>({ [symbol1]: <span class="hljs-number">1</span> }, { [symbol1]: <span class="hljs-number">1</span> });
<span class="hljs-comment">// OK, because it is the same symbol on both objects.</span>
assert.<span class="hljs-title function_">deepStrictEqual</span>({ [symbol1]: <span class="hljs-number">1</span> }, { [symbol2]: <span class="hljs-number">1</span> });
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: Inputs identical but not reference equal:</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// {</span>
<span class="hljs-comment">// [Symbol()]: 1</span>
<span class="hljs-comment">// }</span>
<span class="hljs-keyword">const</span> weakMap1 = <span class="hljs-keyword">new</span> <span class="hljs-title class_">WeakMap</span>();
<span class="hljs-keyword">const</span> weakMap2 = <span class="hljs-keyword">new</span> <span class="hljs-title class_">WeakMap</span>([[{}, {}]]);
<span class="hljs-keyword">const</span> weakMap3 = <span class="hljs-keyword">new</span> <span class="hljs-title class_">WeakMap</span>();
weakMap3.<span class="hljs-property">unequal</span> = <span class="hljs-literal">true</span>;
assert.<span class="hljs-title function_">deepStrictEqual</span>(weakMap1, weakMap2);
<span class="hljs-comment">// OK, because it is impossible to compare the entries</span>
<span class="hljs-comment">// Fails because weakMap3 has a property that weakMap1 does not contain:</span>
assert.<span class="hljs-title function_">deepStrictEqual</span>(weakMap1, weakMap3);
<span class="hljs-comment">// AssertionError: Expected inputs to be strictly deep-equal:</span>
<span class="hljs-comment">// + actual - expected</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// WeakMap {</span>
<span class="hljs-comment">// + [items unknown]</span>
<span class="hljs-comment">// - [items unknown],</span>
<span class="hljs-comment">// - unequal: true</span>
<span class="hljs-comment">// }</span></code><button class="copy-button">copy</button></pre>
<p>If the values are not equal, an <a href="#class-assertassertionerror"><code>AssertionError</code></a> is thrown with a <code>message</code>
property set equal to the value of the <code>message</code> parameter. If the <code>message</code>
parameter is undefined, a default error message is assigned. If the <code>message</code>
parameter is an instance of an <a href="errors.html#class-error"><code>Error</code></a> then it will be thrown instead of the
<code>AssertionError</code>.</p>
</section><section><h3><code>assert.doesNotMatch(string, regexp[, message])</code><span><a class="mark" href="#assertdoesnotmatchstring-regexp-message" id="assertdoesnotmatchstring-regexp-message">#</a></span><a aria-hidden="true" class="legacy" id="assert_assert_doesnotmatch_string_regexp_message"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v16.0.0</td>
<td><p>This API is no longer experimental.</p></td></tr>
<tr><td>v13.6.0, v12.16.0</td>
<td><p><span>Added in: v13.6.0, v12.16.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>string</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
<li><code>regexp</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type"><RegExp></a></li>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li>
</ul>
<p>Expects the <code>string</code> input not to match the regular expression.</p>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
assert.<span class="hljs-title function_">doesNotMatch</span>(<span class="hljs-string">'I will fail'</span>, <span class="hljs-regexp">/fail/</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: The input was expected to not match the ...</span>
assert.<span class="hljs-title function_">doesNotMatch</span>(<span class="hljs-number">123</span>, <span class="hljs-regexp">/pass/</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: The "string" argument must be of type string.</span>
assert.<span class="hljs-title function_">doesNotMatch</span>(<span class="hljs-string">'I will pass'</span>, <span class="hljs-regexp">/different/</span>);
<span class="hljs-comment">// OK</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
assert.<span class="hljs-title function_">doesNotMatch</span>(<span class="hljs-string">'I will fail'</span>, <span class="hljs-regexp">/fail/</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: The input was expected to not match the ...</span>
assert.<span class="hljs-title function_">doesNotMatch</span>(<span class="hljs-number">123</span>, <span class="hljs-regexp">/pass/</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: The "string" argument must be of type string.</span>
assert.<span class="hljs-title function_">doesNotMatch</span>(<span class="hljs-string">'I will pass'</span>, <span class="hljs-regexp">/different/</span>);
<span class="hljs-comment">// OK</span></code><button class="copy-button">copy</button></pre>
<p>If the values do match, or if the <code>string</code> argument is of another type than
<code>string</code>, an <a href="#class-assertassertionerror"><code>AssertionError</code></a> is thrown with a <code>message</code> property set equal
to the value of the <code>message</code> parameter. If the <code>message</code> parameter is
undefined, a default error message is assigned. If the <code>message</code> parameter is an
instance of an <a href="errors.html#class-error"><code>Error</code></a> then it will be thrown instead of the
<a href="#class-assertassertionerror"><code>AssertionError</code></a>.</p>
</section><section><h3><code>assert.doesNotReject(asyncFn[, error][, message])</code><span><a class="mark" href="#assertdoesnotrejectasyncfn-error-message" id="assertdoesnotrejectasyncfn-error-message">#</a></span><a aria-hidden="true" class="legacy" id="assert_assert_doesnotreject_asyncfn_error_message"></a></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>asyncFn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type"><Promise></a></li>
<li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type"><RegExp></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>Awaits the <code>asyncFn</code> promise or, if <code>asyncFn</code> is a function, immediately
calls the function and awaits the returned promise to complete. It will then
check that the promise is not rejected.</p>
<p>If <code>asyncFn</code> is a function and it throws an error synchronously,
<code>assert.doesNotReject()</code> will return a rejected <code>Promise</code> with that error. If
the function does not return a promise, <code>assert.doesNotReject()</code> will return a
rejected <code>Promise</code> with an <a href="errors.html#err_invalid_return_value"><code>ERR_INVALID_RETURN_VALUE</code></a> error. In both cases
the error handler is skipped.</p>
<p>Using <code>assert.doesNotReject()</code> is actually not useful because there is little
benefit in catching a rejection and then rejecting it again. Instead, consider
adding a comment next to the specific code path that should not reject and keep
error messages as expressive as possible.</p>
<p>If specified, <code>error</code> can be a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes"><code>Class</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a>, or a validation
function. See <a href="#assertthrowsfn-error-message"><code>assert.throws()</code></a> for more details.</p>
<p>Besides the async nature to await the completion behaves identically to
<a href="#assertdoesnotthrowfn-error-message"><code>assert.doesNotThrow()</code></a>.</p>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
<span class="hljs-keyword">await</span> assert.<span class="hljs-title function_">doesNotReject</span>(
<span class="hljs-keyword">async</span> () => {
<span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Wrong value'</span>);
},
<span class="hljs-title class_">SyntaxError</span>,
);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
(<span class="hljs-keyword">async</span> () => {
<span class="hljs-keyword">await</span> assert.<span class="hljs-title function_">doesNotReject</span>(
<span class="hljs-keyword">async</span> () => {
<span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Wrong value'</span>);
},
<span class="hljs-title class_">SyntaxError</span>,
);
})();</code><button class="copy-button">copy</button></pre>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
assert.<span class="hljs-title function_">doesNotReject</span>(<span class="hljs-title class_">Promise</span>.<span class="hljs-title function_">reject</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Wrong value'</span>)))
.<span class="hljs-title function_">then</span>(<span class="hljs-function">() =></span> {
<span class="hljs-comment">// ...</span>
});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
assert.<span class="hljs-title function_">doesNotReject</span>(<span class="hljs-title class_">Promise</span>.<span class="hljs-title function_">reject</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Wrong value'</span>)))
.<span class="hljs-title function_">then</span>(<span class="hljs-function">() =></span> {
<span class="hljs-comment">// ...</span>
});</code><button class="copy-button">copy</button></pre>
</section><section><h3><code>assert.doesNotThrow(fn[, error][, message])</code><span><a class="mark" href="#assertdoesnotthrowfn-error-message" id="assertdoesnotthrowfn-error-message">#</a></span><a aria-hidden="true" class="legacy" id="assert_assert_doesnotthrow_fn_error_message"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v5.11.0, v4.4.5</td>
<td><p>The <code>message</code> parameter is respected now.</p></td></tr>
<tr><td>v4.2.0</td>
<td><p>The <code>error</code> parameter can now be an arrow function.</p></td></tr>
<tr><td>v0.1.21</td>
<td><p><span>Added in: v0.1.21</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
<li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type"><RegExp></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>Asserts that the function <code>fn</code> does not throw an error.</p>
<p>Using <code>assert.doesNotThrow()</code> is actually not useful because there
is no benefit in catching an error and then rethrowing it. Instead, consider
adding a comment next to the specific code path that should not throw and keep
error messages as expressive as possible.</p>
<p>When <code>assert.doesNotThrow()</code> is called, it will immediately call the <code>fn</code>
function.</p>
<p>If an error is thrown and it is the same type as that specified by the <code>error</code>
parameter, then an <a href="#class-assertassertionerror"><code>AssertionError</code></a> is thrown. If the error is of a
different type, or if the <code>error</code> parameter is undefined, the error is
propagated back to the caller.</p>
<p>If specified, <code>error</code> can be a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes"><code>Class</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a>, or a validation
function. See <a href="#assertthrowsfn-error-message"><code>assert.throws()</code></a> for more details.</p>
<p>The following, for instance, will throw the <a href="errors.html#class-typeerror"><code>TypeError</code></a> because there is no
matching error type in the assertion:</p>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
assert.<span class="hljs-title function_">doesNotThrow</span>(
<span class="hljs-function">() =></span> {
<span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Wrong value'</span>);
},
<span class="hljs-title class_">SyntaxError</span>,
);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
assert.<span class="hljs-title function_">doesNotThrow</span>(
<span class="hljs-function">() =></span> {
<span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Wrong value'</span>);
},
<span class="hljs-title class_">SyntaxError</span>,
);</code><button class="copy-button">copy</button></pre>
<p>However, the following will result in an <a href="#class-assertassertionerror"><code>AssertionError</code></a> with the message
'Got unwanted exception...':</p>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
assert.<span class="hljs-title function_">doesNotThrow</span>(
<span class="hljs-function">() =></span> {
<span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Wrong value'</span>);
},
<span class="hljs-title class_">TypeError</span>,
);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
assert.<span class="hljs-title function_">doesNotThrow</span>(
<span class="hljs-function">() =></span> {
<span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Wrong value'</span>);
},
<span class="hljs-title class_">TypeError</span>,
);</code><button class="copy-button">copy</button></pre>
<p>If an <a href="#class-assertassertionerror"><code>AssertionError</code></a> is thrown and a value is provided for the <code>message</code>
parameter, the value of <code>message</code> will be appended to the <a href="#class-assertassertionerror"><code>AssertionError</code></a>
message:</p>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
assert.<span class="hljs-title function_">doesNotThrow</span>(
<span class="hljs-function">() =></span> {
<span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Wrong value'</span>);
},
<span class="hljs-regexp">/Wrong value/</span>,
<span class="hljs-string">'Whoops'</span>,
);
<span class="hljs-comment">// Throws: AssertionError: Got unwanted exception: Whoops</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
assert.<span class="hljs-title function_">doesNotThrow</span>(
<span class="hljs-function">() =></span> {
<span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Wrong value'</span>);
},
<span class="hljs-regexp">/Wrong value/</span>,
<span class="hljs-string">'Whoops'</span>,
);
<span class="hljs-comment">// Throws: AssertionError: Got unwanted exception: Whoops</span></code><button class="copy-button">copy</button></pre>
</section><section><h3><code>assert.equal(actual, expected[, message])</code><span><a class="mark" href="#assertequalactual-expected-message" id="assertequalactual-expected-message">#</a></span><a aria-hidden="true" class="legacy" id="assert_assert_equal_actual_expected_message"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v16.0.0, v14.18.0</td>
<td><p>In Legacy assertion mode, changed status from Deprecated to Legacy.</p></td></tr>
<tr><td>v14.0.0</td>
<td><p>NaN is now treated as being identical if both sides are NaN.</p></td></tr>
<tr><td>v0.1.21</td>
<td><p><span>Added in: v0.1.21</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li>
</ul>
<p><strong>Strict assertion mode</strong></p>
<p>An alias of <a href="#assertstrictequalactual-expected-message"><code>assert.strictEqual()</code></a>.</p>
<p><strong>Legacy assertion mode</strong></p>
<p></p><div class="api_stability api_stability_3"><a href="documentation.html#stability-index">Stability: 3</a> - Legacy: Use <a href="#assertstrictequalactual-expected-message"><code>assert.strictEqual()</code></a> instead.</div><p></p>
<p>Tests shallow, coercive equality between the <code>actual</code> and <code>expected</code> parameters
using the <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Equality"><code>==</code> operator</a>. <code>NaN</code> is specially handled
and treated as being identical if both sides are <code>NaN</code>.</p>
<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
assert.<span class="hljs-title function_">equal</span>(<span class="hljs-number">1</span>, <span class="hljs-number">1</span>);
<span class="hljs-comment">// OK, 1 == 1</span>
assert.<span class="hljs-title function_">equal</span>(<span class="hljs-number">1</span>, <span class="hljs-string">'1'</span>);
<span class="hljs-comment">// OK, 1 == '1'</span>
assert.<span class="hljs-title function_">equal</span>(<span class="hljs-title class_">NaN</span>, <span class="hljs-title class_">NaN</span>);
<span class="hljs-comment">// OK</span>
assert.<span class="hljs-title function_">equal</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>);
<span class="hljs-comment">// AssertionError: 1 == 2</span>
assert.<span class="hljs-title function_">equal</span>({ <span class="hljs-attr">a</span>: { <span class="hljs-attr">b</span>: <span class="hljs-number">1</span> } }, { <span class="hljs-attr">a</span>: { <span class="hljs-attr">b</span>: <span class="hljs-number">1</span> } });
<span class="hljs-comment">// AssertionError: { a: { b: 1 } } == { a: { b: 1 } }</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
assert.<span class="hljs-title function_">equal</span>(<span class="hljs-number">1</span>, <span class="hljs-number">1</span>);
<span class="hljs-comment">// OK, 1 == 1</span>
assert.<span class="hljs-title function_">equal</span>(<span class="hljs-number">1</span>, <span class="hljs-string">'1'</span>);
<span class="hljs-comment">// OK, 1 == '1'</span>
assert.<span class="hljs-title function_">equal</span>(<span class="hljs-title class_">NaN</span>, <span class="hljs-title class_">NaN</span>);
<span class="hljs-comment">// OK</span>
assert.<span class="hljs-title function_">equal</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>);
<span class="hljs-comment">// AssertionError: 1 == 2</span>
assert.<span class="hljs-title function_">equal</span>({ <span class="hljs-attr">a</span>: { <span class="hljs-attr">b</span>: <span class="hljs-number">1</span> } }, { <span class="hljs-attr">a</span>: { <span class="hljs-attr">b</span>: <span class="hljs-number">1</span> } });
<span class="hljs-comment">// AssertionError: { a: { b: 1 } } == { a: { b: 1 } }</span></code><button class="copy-button">copy</button></pre>
<p>If the values are not equal, an <a href="#class-assertassertionerror"><code>AssertionError</code></a> is thrown with a <code>message</code>
property set equal to the value of the <code>message</code> parameter. If the <code>message</code>
parameter is undefined, a default error message is assigned. If the <code>message</code>
parameter is an instance of an <a href="errors.html#class-error"><code>Error</code></a> then it will be thrown instead of the
<code>AssertionError</code>.</p>
</section><section><h3><code>assert.fail([message])</code><span><a class="mark" href="#assertfailmessage" id="assertfailmessage">#</a></span><a aria-hidden="true" class="legacy" id="assert_assert_fail_message"></a></h3>
<div class="api_metadata">
<span>Added in: v0.1.21</span>
</div>
<ul>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a> <strong>Default:</strong> <code>'Failed'</code></li>
</ul>
<p>Throws an <a href="#class-assertassertionerror"><code>AssertionError</code></a> with the provided error message or a default
error message. If the <code>message</code> parameter is an instance of an <a href="errors.html#class-error"><code>Error</code></a> then
it will be thrown instead of the <a href="#class-assertassertionerror"><code>AssertionError</code></a>.</p>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
assert.<span class="hljs-title function_">fail</span>();
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: Failed</span>
assert.<span class="hljs-title function_">fail</span>(<span class="hljs-string">'boom'</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: boom</span>
assert.<span class="hljs-title function_">fail</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'need array'</span>));
<span class="hljs-comment">// TypeError: need array</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
assert.<span class="hljs-title function_">fail</span>();
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: Failed</span>
assert.<span class="hljs-title function_">fail</span>(<span class="hljs-string">'boom'</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: boom</span>
assert.<span class="hljs-title function_">fail</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'need array'</span>));
<span class="hljs-comment">// TypeError: need array</span></code><button class="copy-button">copy</button></pre>
<p>Using <code>assert.fail()</code> with more than two arguments is possible but deprecated.
See below for further details.</p>
</section><section><h3><code>assert.fail(actual, expected[, message[, operator[, stackStartFn]]])</code><span><a class="mark" href="#assertfailactual-expected-message-operator-stackstartfn" id="assertfailactual-expected-message-operator-stackstartfn">#</a></span><a aria-hidden="true" class="legacy" id="assert_assert_fail_actual_expected_message_operator_stackstartfn"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v10.0.0</td>
<td><p>Calling <code>assert.fail()</code> with more than one argument is deprecated and emits a warning.</p></td></tr>
<tr><td>v0.1.21</td>
<td><p><span>Added in: v0.1.21</span></p></td></tr>
</tbody></table>
</details>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <code>assert.fail([message])</code> or other assert
functions instead.</div><p></p>
<ul>
<li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li>
<li><code>operator</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> <strong>Default:</strong> <code>'!='</code></li>
<li><code>stackStartFn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> <strong>Default:</strong> <code>assert.fail</code></li>
</ul>
<p>If <code>message</code> is falsy, the error message is set as the values of <code>actual</code> and
<code>expected</code> separated by the provided <code>operator</code>. If just the two <code>actual</code> and
<code>expected</code> arguments are provided, <code>operator</code> will default to <code>'!='</code>. If
<code>message</code> is provided as third argument it will be used as the error message and
the other arguments will be stored as properties on the thrown object. If
<code>stackStartFn</code> is provided, all stack frames above that function will be
removed from stacktrace (see <a href="errors.html#errorcapturestacktracetargetobject-constructoropt"><code>Error.captureStackTrace</code></a>). If no arguments are
given, the default message <code>Failed</code> will be used.</p>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
assert.<span class="hljs-title function_">fail</span>(<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: 'a' != 'b'</span>
assert.<span class="hljs-title function_">fail</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-literal">undefined</span>, <span class="hljs-string">'>'</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: 1 > 2</span>
assert.<span class="hljs-title function_">fail</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-string">'fail'</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: fail</span>
assert.<span class="hljs-title function_">fail</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-string">'whoops'</span>, <span class="hljs-string">'>'</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: whoops</span>
assert.<span class="hljs-title function_">fail</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'need array'</span>));
<span class="hljs-comment">// TypeError: need array</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
assert.<span class="hljs-title function_">fail</span>(<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: 'a' != 'b'</span>
assert.<span class="hljs-title function_">fail</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-literal">undefined</span>, <span class="hljs-string">'>'</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: 1 > 2</span>
assert.<span class="hljs-title function_">fail</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-string">'fail'</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: fail</span>
assert.<span class="hljs-title function_">fail</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-string">'whoops'</span>, <span class="hljs-string">'>'</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: whoops</span>
assert.<span class="hljs-title function_">fail</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'need array'</span>));
<span class="hljs-comment">// TypeError: need array</span></code><button class="copy-button">copy</button></pre>
<p>In the last three cases <code>actual</code>, <code>expected</code>, and <code>operator</code> have no
influence on the error message.</p>
<p>Example use of <code>stackStartFn</code> for truncating the exception's stacktrace:</p>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
<span class="hljs-keyword">function</span> <span class="hljs-title function_">suppressFrame</span>(<span class="hljs-params"></span>) {
assert.<span class="hljs-title function_">fail</span>(<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>, <span class="hljs-literal">undefined</span>, <span class="hljs-string">'!=='</span>, suppressFrame);
}
<span class="hljs-title function_">suppressFrame</span>();
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: 'a' !== 'b'</span>
<span class="hljs-comment">// at repl:1:1</span>
<span class="hljs-comment">// at ContextifyScript.Script.runInThisContext (vm.js:44:33)</span>
<span class="hljs-comment">// ...</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
<span class="hljs-keyword">function</span> <span class="hljs-title function_">suppressFrame</span>(<span class="hljs-params"></span>) {
assert.<span class="hljs-title function_">fail</span>(<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>, <span class="hljs-literal">undefined</span>, <span class="hljs-string">'!=='</span>, suppressFrame);
}
<span class="hljs-title function_">suppressFrame</span>();
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: 'a' !== 'b'</span>
<span class="hljs-comment">// at repl:1:1</span>
<span class="hljs-comment">// at ContextifyScript.Script.runInThisContext (vm.js:44:33)</span>
<span class="hljs-comment">// ...</span></code><button class="copy-button">copy</button></pre>
</section><section><h3><code>assert.ifError(value)</code><span><a class="mark" href="#assertiferrorvalue" id="assertiferrorvalue">#</a></span><a aria-hidden="true" class="legacy" id="assert_assert_iferror_value"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v10.0.0</td>
<td><p>Instead of throwing the original error it is now wrapped into an [<code>AssertionError</code>][] that contains the full stack trace.</p></td></tr>
<tr><td>v10.0.0</td>
<td><p>Value may now only be <code>undefined</code> or <code>null</code>. Before all falsy values were handled the same as <code>null</code> and did not throw.</p></td></tr>
<tr><td>v0.1.97</td>
<td><p><span>Added in: v0.1.97</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
</ul>
<p>Throws <code>value</code> if <code>value</code> is not <code>undefined</code> or <code>null</code>. This is useful when
testing the <code>error</code> argument in callbacks. The stack trace contains all frames
from the error passed to <code>ifError()</code> including the potential new frames for
<code>ifError()</code> itself.</p>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
assert.<span class="hljs-title function_">ifError</span>(<span class="hljs-literal">null</span>);
<span class="hljs-comment">// OK</span>
assert.<span class="hljs-title function_">ifError</span>(<span class="hljs-number">0</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: 0</span>
assert.<span class="hljs-title function_">ifError</span>(<span class="hljs-string">'error'</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: 'error'</span>
assert.<span class="hljs-title function_">ifError</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>());
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: Error</span>
<span class="hljs-comment">// Create some random error frames.</span>
<span class="hljs-keyword">let</span> err;
(<span class="hljs-keyword">function</span> <span class="hljs-title function_">errorFrame</span>(<span class="hljs-params"></span>) {
err = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'test error'</span>);
})();
(<span class="hljs-keyword">function</span> <span class="hljs-title function_">ifErrorFrame</span>(<span class="hljs-params"></span>) {
assert.<span class="hljs-title function_">ifError</span>(err);
})();
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: test error</span>
<span class="hljs-comment">// at ifErrorFrame</span>
<span class="hljs-comment">// at errorFrame</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
assert.<span class="hljs-title function_">ifError</span>(<span class="hljs-literal">null</span>);
<span class="hljs-comment">// OK</span>
assert.<span class="hljs-title function_">ifError</span>(<span class="hljs-number">0</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: 0</span>
assert.<span class="hljs-title function_">ifError</span>(<span class="hljs-string">'error'</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: 'error'</span>
assert.<span class="hljs-title function_">ifError</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>());
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: Error</span>
<span class="hljs-comment">// Create some random error frames.</span>
<span class="hljs-keyword">let</span> err;
(<span class="hljs-keyword">function</span> <span class="hljs-title function_">errorFrame</span>(<span class="hljs-params"></span>) {
err = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'test error'</span>);
})();
(<span class="hljs-keyword">function</span> <span class="hljs-title function_">ifErrorFrame</span>(<span class="hljs-params"></span>) {
assert.<span class="hljs-title function_">ifError</span>(err);
})();
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: ifError got unwanted exception: test error</span>
<span class="hljs-comment">// at ifErrorFrame</span>
<span class="hljs-comment">// at errorFrame</span></code><button class="copy-button">copy</button></pre>
</section><section><h3><code>assert.match(string, regexp[, message])</code><span><a class="mark" href="#assertmatchstring-regexp-message" id="assertmatchstring-regexp-message">#</a></span><a aria-hidden="true" class="legacy" id="assert_assert_match_string_regexp_message"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v16.0.0</td>
<td><p>This API is no longer experimental.</p></td></tr>
<tr><td>v13.6.0, v12.16.0</td>
<td><p><span>Added in: v13.6.0, v12.16.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>string</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
<li><code>regexp</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type"><RegExp></a></li>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li>
</ul>
<p>Expects the <code>string</code> input to match the regular expression.</p>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
assert.<span class="hljs-title function_">match</span>(<span class="hljs-string">'I will fail'</span>, <span class="hljs-regexp">/pass/</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: The input did not match the regular ...</span>
assert.<span class="hljs-title function_">match</span>(<span class="hljs-number">123</span>, <span class="hljs-regexp">/pass/</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: The "string" argument must be of type string.</span>
assert.<span class="hljs-title function_">match</span>(<span class="hljs-string">'I will pass'</span>, <span class="hljs-regexp">/pass/</span>);
<span class="hljs-comment">// OK</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
assert.<span class="hljs-title function_">match</span>(<span class="hljs-string">'I will fail'</span>, <span class="hljs-regexp">/pass/</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: The input did not match the regular ...</span>
assert.<span class="hljs-title function_">match</span>(<span class="hljs-number">123</span>, <span class="hljs-regexp">/pass/</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: The "string" argument must be of type string.</span>
assert.<span class="hljs-title function_">match</span>(<span class="hljs-string">'I will pass'</span>, <span class="hljs-regexp">/pass/</span>);
<span class="hljs-comment">// OK</span></code><button class="copy-button">copy</button></pre>
<p>If the values do not match, or if the <code>string</code> argument is of another type than
<code>string</code>, an <a href="#class-assertassertionerror"><code>AssertionError</code></a> is thrown with a <code>message</code> property set equal
to the value of the <code>message</code> parameter. If the <code>message</code> parameter is
undefined, a default error message is assigned. If the <code>message</code> parameter is an
instance of an <a href="errors.html#class-error"><code>Error</code></a> then it will be thrown instead of the
<a href="#class-assertassertionerror"><code>AssertionError</code></a>.</p>
</section><section><h3><code>assert.notDeepEqual(actual, expected[, message])</code><span><a class="mark" href="#assertnotdeepequalactual-expected-message" id="assertnotdeepequalactual-expected-message">#</a></span><a aria-hidden="true" class="legacy" id="assert_assert_notdeepequal_actual_expected_message"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v16.0.0, v14.18.0</td>
<td><p>In Legacy assertion mode, changed status from Deprecated to Legacy.</p></td></tr>
<tr><td>v14.0.0</td>
<td><p>NaN is now treated as being identical if both sides are NaN.</p></td></tr>
<tr><td>v9.0.0</td>
<td><p>The <code>Error</code> names and messages are now properly compared.</p></td></tr>
<tr><td>v8.0.0</td>
<td><p>The <code>Set</code> and <code>Map</code> content is also compared.</p></td></tr>
<tr><td>v6.4.0, v4.7.1</td>
<td><p>Typed array slices are handled correctly now.</p></td></tr>
<tr><td>v6.1.0, v4.5.0</td>
<td><p>Objects with circular references can be used as inputs now.</p></td></tr>
<tr><td>v5.10.1, v4.4.3</td>
<td><p>Handle non-<code>Uint8Array</code> typed arrays correctly.</p></td></tr>
<tr><td>v0.1.21</td>
<td><p><span>Added in: v0.1.21</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li>
</ul>
<p><strong>Strict assertion mode</strong></p>
<p>An alias of <a href="#assertnotdeepstrictequalactual-expected-message"><code>assert.notDeepStrictEqual()</code></a>.</p>
<p><strong>Legacy assertion mode</strong></p>
<p></p><div class="api_stability api_stability_3"><a href="documentation.html#stability-index">Stability: 3</a> - Legacy: Use <a href="#assertnotdeepstrictequalactual-expected-message"><code>assert.notDeepStrictEqual()</code></a> instead.</div><p></p>
<p>Tests for any deep inequality. Opposite of <a href="#assertdeepequalactual-expected-message"><code>assert.deepEqual()</code></a>.</p>
<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-keyword">const</span> obj1 = {
<span class="hljs-attr">a</span>: {
<span class="hljs-attr">b</span>: <span class="hljs-number">1</span>,
},
};
<span class="hljs-keyword">const</span> obj2 = {
<span class="hljs-attr">a</span>: {
<span class="hljs-attr">b</span>: <span class="hljs-number">2</span>,
},
};
<span class="hljs-keyword">const</span> obj3 = {
<span class="hljs-attr">a</span>: {
<span class="hljs-attr">b</span>: <span class="hljs-number">1</span>,
},
};
<span class="hljs-keyword">const</span> obj4 = { <span class="hljs-attr">__proto__</span>: obj1 };
assert.<span class="hljs-title function_">notDeepEqual</span>(obj1, obj1);
<span class="hljs-comment">// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }</span>
assert.<span class="hljs-title function_">notDeepEqual</span>(obj1, obj2);
<span class="hljs-comment">// OK</span>
assert.<span class="hljs-title function_">notDeepEqual</span>(obj1, obj3);
<span class="hljs-comment">// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }</span>
assert.<span class="hljs-title function_">notDeepEqual</span>(obj1, obj4);
<span class="hljs-comment">// OK</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> obj1 = {
<span class="hljs-attr">a</span>: {
<span class="hljs-attr">b</span>: <span class="hljs-number">1</span>,
},
};
<span class="hljs-keyword">const</span> obj2 = {
<span class="hljs-attr">a</span>: {
<span class="hljs-attr">b</span>: <span class="hljs-number">2</span>,
},
};
<span class="hljs-keyword">const</span> obj3 = {
<span class="hljs-attr">a</span>: {
<span class="hljs-attr">b</span>: <span class="hljs-number">1</span>,
},
};
<span class="hljs-keyword">const</span> obj4 = { <span class="hljs-attr">__proto__</span>: obj1 };
assert.<span class="hljs-title function_">notDeepEqual</span>(obj1, obj1);
<span class="hljs-comment">// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }</span>
assert.<span class="hljs-title function_">notDeepEqual</span>(obj1, obj2);
<span class="hljs-comment">// OK</span>
assert.<span class="hljs-title function_">notDeepEqual</span>(obj1, obj3);
<span class="hljs-comment">// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }</span>
assert.<span class="hljs-title function_">notDeepEqual</span>(obj1, obj4);
<span class="hljs-comment">// OK</span></code><button class="copy-button">copy</button></pre>
<p>If the values are deeply equal, an <a href="#class-assertassertionerror"><code>AssertionError</code></a> is thrown with a
<code>message</code> property set equal to the value of the <code>message</code> parameter. If the
<code>message</code> parameter is undefined, a default error message is assigned. If the
<code>message</code> parameter is an instance of an <a href="errors.html#class-error"><code>Error</code></a> then it will be thrown
instead of the <code>AssertionError</code>.</p>
</section><section><h3><code>assert.notDeepStrictEqual(actual, expected[, message])</code><span><a class="mark" href="#assertnotdeepstrictequalactual-expected-message" id="assertnotdeepstrictequalactual-expected-message">#</a></span><a aria-hidden="true" class="legacy" id="assert_assert_notdeepstrictequal_actual_expected_message"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v9.0.0</td>
<td><p>The <code>-0</code> and <code>+0</code> are not considered equal anymore.</p></td></tr>
<tr><td>v9.0.0</td>
<td><p>The <code>NaN</code> is now compared using the <a href="https://tc39.github.io/ecma262/#sec-samevaluezero">SameValueZero</a> comparison.</p></td></tr>
<tr><td>v9.0.0</td>
<td><p>The <code>Error</code> names and messages are now properly compared.</p></td></tr>
<tr><td>v8.0.0</td>
<td><p>The <code>Set</code> and <code>Map</code> content is also compared.</p></td></tr>
<tr><td>v6.1.0</td>
<td><p>Objects with circular references can be used as inputs now.</p></td></tr>
<tr><td>v6.4.0, v4.7.1</td>
<td><p>Typed array slices are handled correctly now.</p></td></tr>
<tr><td>v5.10.1, v4.4.3</td>
<td><p>Handle non-<code>Uint8Array</code> typed arrays correctly.</p></td></tr>
<tr><td>v1.2.0</td>
<td><p><span>Added in: v1.2.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li>
</ul>
<p>Tests for deep strict inequality. Opposite of <a href="#assertdeepstrictequalactual-expected-message"><code>assert.deepStrictEqual()</code></a>.</p>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
assert.<span class="hljs-title function_">notDeepStrictEqual</span>({ <span class="hljs-attr">a</span>: <span class="hljs-number">1</span> }, { <span class="hljs-attr">a</span>: <span class="hljs-string">'1'</span> });
<span class="hljs-comment">// OK</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
assert.<span class="hljs-title function_">notDeepStrictEqual</span>({ <span class="hljs-attr">a</span>: <span class="hljs-number">1</span> }, { <span class="hljs-attr">a</span>: <span class="hljs-string">'1'</span> });
<span class="hljs-comment">// OK</span></code><button class="copy-button">copy</button></pre>
<p>If the values are deeply and strictly equal, an <a href="#class-assertassertionerror"><code>AssertionError</code></a> is thrown
with a <code>message</code> property set equal to the value of the <code>message</code> parameter. If
the <code>message</code> parameter is undefined, a default error message is assigned. If
the <code>message</code> parameter is an instance of an <a href="errors.html#class-error"><code>Error</code></a> then it will be thrown
instead of the <a href="#class-assertassertionerror"><code>AssertionError</code></a>.</p>
</section><section><h3><code>assert.notEqual(actual, expected[, message])</code><span><a class="mark" href="#assertnotequalactual-expected-message" id="assertnotequalactual-expected-message">#</a></span><a aria-hidden="true" class="legacy" id="assert_assert_notequal_actual_expected_message"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v16.0.0, v14.18.0</td>
<td><p>In Legacy assertion mode, changed status from Deprecated to Legacy.</p></td></tr>
<tr><td>v14.0.0</td>
<td><p>NaN is now treated as being identical if both sides are NaN.</p></td></tr>
<tr><td>v0.1.21</td>
<td><p><span>Added in: v0.1.21</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li>
</ul>
<p><strong>Strict assertion mode</strong></p>
<p>An alias of <a href="#assertnotstrictequalactual-expected-message"><code>assert.notStrictEqual()</code></a>.</p>
<p><strong>Legacy assertion mode</strong></p>
<p></p><div class="api_stability api_stability_3"><a href="documentation.html#stability-index">Stability: 3</a> - Legacy: Use <a href="#assertnotstrictequalactual-expected-message"><code>assert.notStrictEqual()</code></a> instead.</div><p></p>
<p>Tests shallow, coercive inequality with the <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Inequality"><code>!=</code> operator</a>. <code>NaN</code> is
specially handled and treated as being identical if both sides are <code>NaN</code>.</p>
<pre class="with-38-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
assert.<span class="hljs-title function_">notEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>);
<span class="hljs-comment">// OK</span>
assert.<span class="hljs-title function_">notEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">1</span>);
<span class="hljs-comment">// AssertionError: 1 != 1</span>
assert.<span class="hljs-title function_">notEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-string">'1'</span>);
<span class="hljs-comment">// AssertionError: 1 != '1'</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
assert.<span class="hljs-title function_">notEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>);
<span class="hljs-comment">// OK</span>
assert.<span class="hljs-title function_">notEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">1</span>);
<span class="hljs-comment">// AssertionError: 1 != 1</span>
assert.<span class="hljs-title function_">notEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-string">'1'</span>);
<span class="hljs-comment">// AssertionError: 1 != '1'</span></code><button class="copy-button">copy</button></pre>
<p>If the values are equal, an <a href="#class-assertassertionerror"><code>AssertionError</code></a> is thrown with a <code>message</code>
property set equal to the value of the <code>message</code> parameter. If the <code>message</code>
parameter is undefined, a default error message is assigned. If the <code>message</code>
parameter is an instance of an <a href="errors.html#class-error"><code>Error</code></a> then it will be thrown instead of the
<code>AssertionError</code>.</p>
</section><section><h3><code>assert.notStrictEqual(actual, expected[, message])</code><span><a class="mark" href="#assertnotstrictequalactual-expected-message" id="assertnotstrictequalactual-expected-message">#</a></span><a aria-hidden="true" class="legacy" id="assert_assert_notstrictequal_actual_expected_message"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v10.0.0</td>
<td><p>Used comparison changed from Strict Equality to <code>Object.is()</code>.</p></td></tr>
<tr><td>v0.1.21</td>
<td><p><span>Added in: v0.1.21</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li>
</ul>
<p>Tests strict inequality between the <code>actual</code> and <code>expected</code> parameters as
determined by <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is"><code>Object.is()</code></a>.</p>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
assert.<span class="hljs-title function_">notStrictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>);
<span class="hljs-comment">// OK</span>
assert.<span class="hljs-title function_">notStrictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">1</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: Expected "actual" to be strictly unequal to:</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// 1</span>
assert.<span class="hljs-title function_">notStrictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-string">'1'</span>);
<span class="hljs-comment">// OK</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
assert.<span class="hljs-title function_">notStrictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>);
<span class="hljs-comment">// OK</span>
assert.<span class="hljs-title function_">notStrictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">1</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: Expected "actual" to be strictly unequal to:</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// 1</span>
assert.<span class="hljs-title function_">notStrictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-string">'1'</span>);
<span class="hljs-comment">// OK</span></code><button class="copy-button">copy</button></pre>
<p>If the values are strictly equal, an <a href="#class-assertassertionerror"><code>AssertionError</code></a> is thrown with a
<code>message</code> property set equal to the value of the <code>message</code> parameter. If the
<code>message</code> parameter is undefined, a default error message is assigned. If the
<code>message</code> parameter is an instance of an <a href="errors.html#class-error"><code>Error</code></a> then it will be thrown
instead of the <code>AssertionError</code>.</p>
</section><section><h3><code>assert.ok(value[, message])</code><span><a class="mark" href="#assertokvalue-message" id="assertokvalue-message">#</a></span><a aria-hidden="true" class="legacy" id="assert_assert_ok_value_message"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v10.0.0</td>
<td><p>The <code>assert.ok()</code> (no arguments) will now use a predefined error message.</p></td></tr>
<tr><td>v0.1.21</td>
<td><p><span>Added in: v0.1.21</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li>
</ul>
<p>Tests if <code>value</code> is truthy. It is equivalent to
<code>assert.equal(!!value, true, message)</code>.</p>
<p>If <code>value</code> is not truthy, an <a href="#class-assertassertionerror"><code>AssertionError</code></a> is thrown with a <code>message</code>
property set equal to the value of the <code>message</code> parameter. If the <code>message</code>
parameter is <code>undefined</code>, a default error message is assigned. If the <code>message</code>
parameter is an instance of an <a href="errors.html#class-error"><code>Error</code></a> then it will be thrown instead of the
<code>AssertionError</code>.
If no arguments are passed in at all <code>message</code> will be set to the string:
<code>'No value argument passed to `assert.ok()`'</code>.</p>
<p>Be aware that in the <code>repl</code> the error message will be different to the one
thrown in a file! See below for further details.</p>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
assert.<span class="hljs-title function_">ok</span>(<span class="hljs-literal">true</span>);
<span class="hljs-comment">// OK</span>
assert.<span class="hljs-title function_">ok</span>(<span class="hljs-number">1</span>);
<span class="hljs-comment">// OK</span>
assert.<span class="hljs-title function_">ok</span>();
<span class="hljs-comment">// AssertionError: No value argument passed to `assert.ok()`</span>
assert.<span class="hljs-title function_">ok</span>(<span class="hljs-literal">false</span>, <span class="hljs-string">'it\'s false'</span>);
<span class="hljs-comment">// AssertionError: it's false</span>
<span class="hljs-comment">// In the repl:</span>
assert.<span class="hljs-title function_">ok</span>(<span class="hljs-keyword">typeof</span> <span class="hljs-number">123</span> === <span class="hljs-string">'string'</span>);
<span class="hljs-comment">// AssertionError: false == true</span>
<span class="hljs-comment">// In a file (e.g. test.js):</span>
assert.<span class="hljs-title function_">ok</span>(<span class="hljs-keyword">typeof</span> <span class="hljs-number">123</span> === <span class="hljs-string">'string'</span>);
<span class="hljs-comment">// AssertionError: The expression evaluated to a falsy value:</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// assert.ok(typeof 123 === 'string')</span>
assert.<span class="hljs-title function_">ok</span>(<span class="hljs-literal">false</span>);
<span class="hljs-comment">// AssertionError: The expression evaluated to a falsy value:</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// assert.ok(false)</span>
assert.<span class="hljs-title function_">ok</span>(<span class="hljs-number">0</span>);
<span class="hljs-comment">// AssertionError: The expression evaluated to a falsy value:</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// assert.ok(0)</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
assert.<span class="hljs-title function_">ok</span>(<span class="hljs-literal">true</span>);
<span class="hljs-comment">// OK</span>
assert.<span class="hljs-title function_">ok</span>(<span class="hljs-number">1</span>);
<span class="hljs-comment">// OK</span>
assert.<span class="hljs-title function_">ok</span>();
<span class="hljs-comment">// AssertionError: No value argument passed to `assert.ok()`</span>
assert.<span class="hljs-title function_">ok</span>(<span class="hljs-literal">false</span>, <span class="hljs-string">'it\'s false'</span>);
<span class="hljs-comment">// AssertionError: it's false</span>
<span class="hljs-comment">// In the repl:</span>
assert.<span class="hljs-title function_">ok</span>(<span class="hljs-keyword">typeof</span> <span class="hljs-number">123</span> === <span class="hljs-string">'string'</span>);
<span class="hljs-comment">// AssertionError: false == true</span>
<span class="hljs-comment">// In a file (e.g. test.js):</span>
assert.<span class="hljs-title function_">ok</span>(<span class="hljs-keyword">typeof</span> <span class="hljs-number">123</span> === <span class="hljs-string">'string'</span>);
<span class="hljs-comment">// AssertionError: The expression evaluated to a falsy value:</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// assert.ok(typeof 123 === 'string')</span>
assert.<span class="hljs-title function_">ok</span>(<span class="hljs-literal">false</span>);
<span class="hljs-comment">// AssertionError: The expression evaluated to a falsy value:</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// assert.ok(false)</span>
assert.<span class="hljs-title function_">ok</span>(<span class="hljs-number">0</span>);
<span class="hljs-comment">// AssertionError: The expression evaluated to a falsy value:</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// assert.ok(0)</span></code><button class="copy-button">copy</button></pre>
<pre class="with-40-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
<span class="hljs-comment">// Using `assert()` works the same:</span>
<span class="hljs-title function_">assert</span>(<span class="hljs-number">0</span>);
<span class="hljs-comment">// AssertionError: The expression evaluated to a falsy value:</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// assert(0)</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-comment">// Using `assert()` works the same:</span>
<span class="hljs-title function_">assert</span>(<span class="hljs-number">0</span>);
<span class="hljs-comment">// AssertionError: The expression evaluated to a falsy value:</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// assert(0)</span></code><button class="copy-button">copy</button></pre>
</section><section><h3><code>assert.rejects(asyncFn[, error][, message])</code><span><a class="mark" href="#assertrejectsasyncfn-error-message" id="assertrejectsasyncfn-error-message">#</a></span><a aria-hidden="true" class="legacy" id="assert_assert_rejects_asyncfn_error_message"></a></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>asyncFn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type"><Promise></a></li>
<li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type"><RegExp></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>Awaits the <code>asyncFn</code> promise or, if <code>asyncFn</code> is a function, immediately
calls the function and awaits the returned promise to complete. It will then
check that the promise is rejected.</p>
<p>If <code>asyncFn</code> is a function and it throws an error synchronously,
<code>assert.rejects()</code> will return a rejected <code>Promise</code> with that error. If the
function does not return a promise, <code>assert.rejects()</code> will return a rejected
<code>Promise</code> with an <a href="errors.html#err_invalid_return_value"><code>ERR_INVALID_RETURN_VALUE</code></a> error. In both cases the error
handler is skipped.</p>
<p>Besides the async nature to await the completion behaves identically to
<a href="#assertthrowsfn-error-message"><code>assert.throws()</code></a>.</p>
<p>If specified, <code>error</code> can be a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes"><code>Class</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a>, a validation function,
an object where each property will be tested for, or an instance of error where
each property will be tested for including the non-enumerable <code>message</code> and
<code>name</code> properties.</p>
<p>If specified, <code>message</code> will be the message provided by the <a href="#class-assertassertionerror"><code>AssertionError</code></a>
if the <code>asyncFn</code> fails to reject.</p>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
<span class="hljs-keyword">await</span> assert.<span class="hljs-title function_">rejects</span>(
<span class="hljs-keyword">async</span> () => {
<span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Wrong value'</span>);
},
{
<span class="hljs-attr">name</span>: <span class="hljs-string">'TypeError'</span>,
<span class="hljs-attr">message</span>: <span class="hljs-string">'Wrong value'</span>,
},
);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
(<span class="hljs-keyword">async</span> () => {
<span class="hljs-keyword">await</span> assert.<span class="hljs-title function_">rejects</span>(
<span class="hljs-keyword">async</span> () => {
<span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Wrong value'</span>);
},
{
<span class="hljs-attr">name</span>: <span class="hljs-string">'TypeError'</span>,
<span class="hljs-attr">message</span>: <span class="hljs-string">'Wrong value'</span>,
},
);
})();</code><button class="copy-button">copy</button></pre>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
<span class="hljs-keyword">await</span> assert.<span class="hljs-title function_">rejects</span>(
<span class="hljs-keyword">async</span> () => {
<span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Wrong value'</span>);
},
<span class="hljs-function">(<span class="hljs-params">err</span>) =></span> {
assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">name</span>, <span class="hljs-string">'TypeError'</span>);
assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">message</span>, <span class="hljs-string">'Wrong value'</span>);
<span class="hljs-keyword">return</span> <span class="hljs-literal">true</span>;
},
);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
(<span class="hljs-keyword">async</span> () => {
<span class="hljs-keyword">await</span> assert.<span class="hljs-title function_">rejects</span>(
<span class="hljs-keyword">async</span> () => {
<span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Wrong value'</span>);
},
<span class="hljs-function">(<span class="hljs-params">err</span>) =></span> {
assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">name</span>, <span class="hljs-string">'TypeError'</span>);
assert.<span class="hljs-title function_">strictEqual</span>(err.<span class="hljs-property">message</span>, <span class="hljs-string">'Wrong value'</span>);
<span class="hljs-keyword">return</span> <span class="hljs-literal">true</span>;
},
);
})();</code><button class="copy-button">copy</button></pre>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
assert.<span class="hljs-title function_">rejects</span>(
<span class="hljs-title class_">Promise</span>.<span class="hljs-title function_">reject</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'Wrong value'</span>)),
<span class="hljs-title class_">Error</span>,
).<span class="hljs-title function_">then</span>(<span class="hljs-function">() =></span> {
<span class="hljs-comment">// ...</span>
});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
assert.<span class="hljs-title function_">rejects</span>(
<span class="hljs-title class_">Promise</span>.<span class="hljs-title function_">reject</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'Wrong value'</span>)),
<span class="hljs-title class_">Error</span>,
).<span class="hljs-title function_">then</span>(<span class="hljs-function">() =></span> {
<span class="hljs-comment">// ...</span>
});</code><button class="copy-button">copy</button></pre>
<p><code>error</code> cannot be a string. If a string is provided as the second
argument, then <code>error</code> is assumed to be omitted and the string will be used for
<code>message</code> instead. This can lead to easy-to-miss mistakes. Please read the
example in <a href="#assertthrowsfn-error-message"><code>assert.throws()</code></a> carefully if using a string as the second
argument gets considered.</p>
</section><section><h3><code>assert.strictEqual(actual, expected[, message])</code><span><a class="mark" href="#assertstrictequalactual-expected-message" id="assertstrictequalactual-expected-message">#</a></span><a aria-hidden="true" class="legacy" id="assert_assert_strictequal_actual_expected_message"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v10.0.0</td>
<td><p>Used comparison changed from Strict Equality to <code>Object.is()</code>.</p></td></tr>
<tr><td>v0.1.21</td>
<td><p><span>Added in: v0.1.21</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>actual</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li><code>expected</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li>
</ul>
<p>Tests strict equality between the <code>actual</code> and <code>expected</code> parameters as
determined by <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is"><code>Object.is()</code></a>.</p>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal:</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// 1 !== 2</span>
assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">1</span>);
<span class="hljs-comment">// OK</span>
assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-string">'Hello foobar'</span>, <span class="hljs-string">'Hello World!'</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal:</span>
<span class="hljs-comment">// + actual - expected</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// + 'Hello foobar'</span>
<span class="hljs-comment">// - 'Hello World!'</span>
<span class="hljs-comment">// ^</span>
<span class="hljs-keyword">const</span> apples = <span class="hljs-number">1</span>;
<span class="hljs-keyword">const</span> oranges = <span class="hljs-number">2</span>;
assert.<span class="hljs-title function_">strictEqual</span>(apples, oranges, <span class="hljs-string">`apples <span class="hljs-subst">${apples}</span> !== oranges <span class="hljs-subst">${oranges}</span>`</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: apples 1 !== oranges 2</span>
assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-string">'1'</span>, <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Inputs are not identical'</span>));
<span class="hljs-comment">// TypeError: Inputs are not identical</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal:</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// 1 !== 2</span>
assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-number">1</span>);
<span class="hljs-comment">// OK</span>
assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-string">'Hello foobar'</span>, <span class="hljs-string">'Hello World!'</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: Expected inputs to be strictly equal:</span>
<span class="hljs-comment">// + actual - expected</span>
<span class="hljs-comment">//</span>
<span class="hljs-comment">// + 'Hello foobar'</span>
<span class="hljs-comment">// - 'Hello World!'</span>
<span class="hljs-comment">// ^</span>
<span class="hljs-keyword">const</span> apples = <span class="hljs-number">1</span>;
<span class="hljs-keyword">const</span> oranges = <span class="hljs-number">2</span>;
assert.<span class="hljs-title function_">strictEqual</span>(apples, oranges, <span class="hljs-string">`apples <span class="hljs-subst">${apples}</span> !== oranges <span class="hljs-subst">${oranges}</span>`</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: apples 1 !== oranges 2</span>
assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-number">1</span>, <span class="hljs-string">'1'</span>, <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Inputs are not identical'</span>));
<span class="hljs-comment">// TypeError: Inputs are not identical</span></code><button class="copy-button">copy</button></pre>
<p>If the values are not strictly equal, an <a href="#class-assertassertionerror"><code>AssertionError</code></a> is thrown with a
<code>message</code> property set equal to the value of the <code>message</code> parameter. If the
<code>message</code> parameter is undefined, a default error message is assigned. If the
<code>message</code> parameter is an instance of an <a href="errors.html#class-error"><code>Error</code></a> then it will be thrown
instead of the <a href="#class-assertassertionerror"><code>AssertionError</code></a>.</p>
</section><section><h3><code>assert.throws(fn[, error][, message])</code><span><a class="mark" href="#assertthrowsfn-error-message" id="assertthrowsfn-error-message">#</a></span><a aria-hidden="true" class="legacy" id="assert_assert_throws_fn_error_message"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v10.2.0</td>
<td><p>The <code>error</code> parameter can be an object containing regular expressions now.</p></td></tr>
<tr><td>v9.9.0</td>
<td><p>The <code>error</code> parameter can now be an object as well.</p></td></tr>
<tr><td>v4.2.0</td>
<td><p>The <code>error</code> parameter can now be an arrow function.</p></td></tr>
<tr><td>v0.1.21</td>
<td><p><span>Added in: v0.1.21</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
<li><code>error</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" class="type"><RegExp></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>Expects the function <code>fn</code> to throw an error.</p>
<p>If specified, <code>error</code> can be a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes"><code>Class</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a>, a validation function,
a validation object where each property will be tested for strict deep equality,
or an instance of error where each property will be tested for strict deep
equality including the non-enumerable <code>message</code> and <code>name</code> properties. When
using an object, it is also possible to use a regular expression, when
validating against a string property. See below for examples.</p>
<p>If specified, <code>message</code> will be appended to the message provided by the
<code>AssertionError</code> if the <code>fn</code> call fails to throw or in case the error validation
fails.</p>
<p>Custom validation object/error instance:</p>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
<span class="hljs-keyword">const</span> err = <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Wrong value'</span>);
err.<span class="hljs-property">code</span> = <span class="hljs-number">404</span>;
err.<span class="hljs-property">foo</span> = <span class="hljs-string">'bar'</span>;
err.<span class="hljs-property">info</span> = {
<span class="hljs-attr">nested</span>: <span class="hljs-literal">true</span>,
<span class="hljs-attr">baz</span>: <span class="hljs-string">'text'</span>,
};
err.<span class="hljs-property">reg</span> = <span class="hljs-regexp">/abc/i</span>;
assert.<span class="hljs-title function_">throws</span>(
<span class="hljs-function">() =></span> {
<span class="hljs-keyword">throw</span> err;
},
{
<span class="hljs-attr">name</span>: <span class="hljs-string">'TypeError'</span>,
<span class="hljs-attr">message</span>: <span class="hljs-string">'Wrong value'</span>,
<span class="hljs-attr">info</span>: {
<span class="hljs-attr">nested</span>: <span class="hljs-literal">true</span>,
<span class="hljs-attr">baz</span>: <span class="hljs-string">'text'</span>,
},
<span class="hljs-comment">// Only properties on the validation object will be tested for.</span>
<span class="hljs-comment">// Using nested objects requires all properties to be present. Otherwise</span>
<span class="hljs-comment">// the validation is going to fail.</span>
},
);
<span class="hljs-comment">// Using regular expressions to validate error properties:</span>
assert.<span class="hljs-title function_">throws</span>(
<span class="hljs-function">() =></span> {
<span class="hljs-keyword">throw</span> err;
},
{
<span class="hljs-comment">// The `name` and `message` properties are strings and using regular</span>
<span class="hljs-comment">// expressions on those will match against the string. If they fail, an</span>
<span class="hljs-comment">// error is thrown.</span>
<span class="hljs-attr">name</span>: <span class="hljs-regexp">/^TypeError$/</span>,
<span class="hljs-attr">message</span>: <span class="hljs-regexp">/Wrong/</span>,
<span class="hljs-attr">foo</span>: <span class="hljs-string">'bar'</span>,
<span class="hljs-attr">info</span>: {
<span class="hljs-attr">nested</span>: <span class="hljs-literal">true</span>,
<span class="hljs-comment">// It is not possible to use regular expressions for nested properties!</span>
<span class="hljs-attr">baz</span>: <span class="hljs-string">'text'</span>,
},
<span class="hljs-comment">// The `reg` property contains a regular expression and only if the</span>
<span class="hljs-comment">// validation object contains an identical regular expression, it is going</span>
<span class="hljs-comment">// to pass.</span>
<span class="hljs-attr">reg</span>: <span class="hljs-regexp">/abc/i</span>,
},
);
<span class="hljs-comment">// Fails due to the different `message` and `name` properties:</span>
assert.<span class="hljs-title function_">throws</span>(
<span class="hljs-function">() =></span> {
<span class="hljs-keyword">const</span> otherErr = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'Not found'</span>);
<span class="hljs-comment">// Copy all enumerable properties from `err` to `otherErr`.</span>
<span class="hljs-keyword">for</span> (<span class="hljs-keyword">const</span> [key, value] <span class="hljs-keyword">of</span> <span class="hljs-title class_">Object</span>.<span class="hljs-title function_">entries</span>(err)) {
otherErr[key] = value;
}
<span class="hljs-keyword">throw</span> otherErr;
},
<span class="hljs-comment">// The error's `message` and `name` properties will also be checked when using</span>
<span class="hljs-comment">// an error as validation object.</span>
err,
);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
<span class="hljs-keyword">const</span> err = <span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>(<span class="hljs-string">'Wrong value'</span>);
err.<span class="hljs-property">code</span> = <span class="hljs-number">404</span>;
err.<span class="hljs-property">foo</span> = <span class="hljs-string">'bar'</span>;
err.<span class="hljs-property">info</span> = {
<span class="hljs-attr">nested</span>: <span class="hljs-literal">true</span>,
<span class="hljs-attr">baz</span>: <span class="hljs-string">'text'</span>,
};
err.<span class="hljs-property">reg</span> = <span class="hljs-regexp">/abc/i</span>;
assert.<span class="hljs-title function_">throws</span>(
<span class="hljs-function">() =></span> {
<span class="hljs-keyword">throw</span> err;
},
{
<span class="hljs-attr">name</span>: <span class="hljs-string">'TypeError'</span>,
<span class="hljs-attr">message</span>: <span class="hljs-string">'Wrong value'</span>,
<span class="hljs-attr">info</span>: {
<span class="hljs-attr">nested</span>: <span class="hljs-literal">true</span>,
<span class="hljs-attr">baz</span>: <span class="hljs-string">'text'</span>,
},
<span class="hljs-comment">// Only properties on the validation object will be tested for.</span>
<span class="hljs-comment">// Using nested objects requires all properties to be present. Otherwise</span>
<span class="hljs-comment">// the validation is going to fail.</span>
},
);
<span class="hljs-comment">// Using regular expressions to validate error properties:</span>
assert.<span class="hljs-title function_">throws</span>(
<span class="hljs-function">() =></span> {
<span class="hljs-keyword">throw</span> err;
},
{
<span class="hljs-comment">// The `name` and `message` properties are strings and using regular</span>
<span class="hljs-comment">// expressions on those will match against the string. If they fail, an</span>
<span class="hljs-comment">// error is thrown.</span>
<span class="hljs-attr">name</span>: <span class="hljs-regexp">/^TypeError$/</span>,
<span class="hljs-attr">message</span>: <span class="hljs-regexp">/Wrong/</span>,
<span class="hljs-attr">foo</span>: <span class="hljs-string">'bar'</span>,
<span class="hljs-attr">info</span>: {
<span class="hljs-attr">nested</span>: <span class="hljs-literal">true</span>,
<span class="hljs-comment">// It is not possible to use regular expressions for nested properties!</span>
<span class="hljs-attr">baz</span>: <span class="hljs-string">'text'</span>,
},
<span class="hljs-comment">// The `reg` property contains a regular expression and only if the</span>
<span class="hljs-comment">// validation object contains an identical regular expression, it is going</span>
<span class="hljs-comment">// to pass.</span>
<span class="hljs-attr">reg</span>: <span class="hljs-regexp">/abc/i</span>,
},
);
<span class="hljs-comment">// Fails due to the different `message` and `name` properties:</span>
assert.<span class="hljs-title function_">throws</span>(
<span class="hljs-function">() =></span> {
<span class="hljs-keyword">const</span> otherErr = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'Not found'</span>);
<span class="hljs-comment">// Copy all enumerable properties from `err` to `otherErr`.</span>
<span class="hljs-keyword">for</span> (<span class="hljs-keyword">const</span> [key, value] <span class="hljs-keyword">of</span> <span class="hljs-title class_">Object</span>.<span class="hljs-title function_">entries</span>(err)) {
otherErr[key] = value;
}
<span class="hljs-keyword">throw</span> otherErr;
},
<span class="hljs-comment">// The error's `message` and `name` properties will also be checked when using</span>
<span class="hljs-comment">// an error as validation object.</span>
err,
);</code><button class="copy-button">copy</button></pre>
<p>Validate instanceof using constructor:</p>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
assert.<span class="hljs-title function_">throws</span>(
<span class="hljs-function">() =></span> {
<span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'Wrong value'</span>);
},
<span class="hljs-title class_">Error</span>,
);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
assert.<span class="hljs-title function_">throws</span>(
<span class="hljs-function">() =></span> {
<span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'Wrong value'</span>);
},
<span class="hljs-title class_">Error</span>,
);</code><button class="copy-button">copy</button></pre>
<p>Validate error message using <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions"><code>RegExp</code></a>:</p>
<p>Using a regular expression runs <code>.toString</code> on the error object, and will
therefore also include the error name.</p>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
assert.<span class="hljs-title function_">throws</span>(
<span class="hljs-function">() =></span> {
<span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'Wrong value'</span>);
},
<span class="hljs-regexp">/^Error: Wrong value$/</span>,
);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
assert.<span class="hljs-title function_">throws</span>(
<span class="hljs-function">() =></span> {
<span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'Wrong value'</span>);
},
<span class="hljs-regexp">/^Error: Wrong value$/</span>,
);</code><button class="copy-button">copy</button></pre>
<p>Custom error validation:</p>
<p>The function must return <code>true</code> to indicate all internal validations passed.
It will otherwise fail with an <a href="#class-assertassertionerror"><code>AssertionError</code></a>.</p>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
assert.<span class="hljs-title function_">throws</span>(
<span class="hljs-function">() =></span> {
<span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'Wrong value'</span>);
},
<span class="hljs-function">(<span class="hljs-params">err</span>) =></span> {
<span class="hljs-title function_">assert</span>(err <span class="hljs-keyword">instanceof</span> <span class="hljs-title class_">Error</span>);
<span class="hljs-title function_">assert</span>(<span class="hljs-regexp">/value/</span>.<span class="hljs-title function_">test</span>(err));
<span class="hljs-comment">// Avoid returning anything from validation functions besides `true`.</span>
<span class="hljs-comment">// Otherwise, it's not clear what part of the validation failed. Instead,</span>
<span class="hljs-comment">// throw an error about the specific validation that failed (as done in this</span>
<span class="hljs-comment">// example) and add as much helpful debugging information to that error as</span>
<span class="hljs-comment">// possible.</span>
<span class="hljs-keyword">return</span> <span class="hljs-literal">true</span>;
},
<span class="hljs-string">'unexpected error'</span>,
);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
assert.<span class="hljs-title function_">throws</span>(
<span class="hljs-function">() =></span> {
<span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'Wrong value'</span>);
},
<span class="hljs-function">(<span class="hljs-params">err</span>) =></span> {
<span class="hljs-title function_">assert</span>(err <span class="hljs-keyword">instanceof</span> <span class="hljs-title class_">Error</span>);
<span class="hljs-title function_">assert</span>(<span class="hljs-regexp">/value/</span>.<span class="hljs-title function_">test</span>(err));
<span class="hljs-comment">// Avoid returning anything from validation functions besides `true`.</span>
<span class="hljs-comment">// Otherwise, it's not clear what part of the validation failed. Instead,</span>
<span class="hljs-comment">// throw an error about the specific validation that failed (as done in this</span>
<span class="hljs-comment">// example) and add as much helpful debugging information to that error as</span>
<span class="hljs-comment">// possible.</span>
<span class="hljs-keyword">return</span> <span class="hljs-literal">true</span>;
},
<span class="hljs-string">'unexpected error'</span>,
);</code><button class="copy-button">copy</button></pre>
<p><code>error</code> cannot be a string. If a string is provided as the second
argument, then <code>error</code> is assumed to be omitted and the string will be used for
<code>message</code> instead. This can lead to easy-to-miss mistakes. Using the same
message as the thrown error message is going to result in an
<code>ERR_AMBIGUOUS_ARGUMENT</code> error. Please read the example below carefully if using
a string as the second argument gets considered:</p>
<pre class="with-45-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert/strict'</span>;
<span class="hljs-keyword">function</span> <span class="hljs-title function_">throwingFirst</span>(<span class="hljs-params"></span>) {
<span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'First'</span>);
}
<span class="hljs-keyword">function</span> <span class="hljs-title function_">throwingSecond</span>(<span class="hljs-params"></span>) {
<span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'Second'</span>);
}
<span class="hljs-keyword">function</span> <span class="hljs-title function_">notThrowing</span>(<span class="hljs-params"></span>) {}
<span class="hljs-comment">// The second argument is a string and the input function threw an Error.</span>
<span class="hljs-comment">// The first case will not throw as it does not match for the error message</span>
<span class="hljs-comment">// thrown by the input function!</span>
assert.<span class="hljs-title function_">throws</span>(throwingFirst, <span class="hljs-string">'Second'</span>);
<span class="hljs-comment">// In the next example the message has no benefit over the message from the</span>
<span class="hljs-comment">// error and since it is not clear if the user intended to actually match</span>
<span class="hljs-comment">// against the error message, Node.js throws an `ERR_AMBIGUOUS_ARGUMENT` error.</span>
assert.<span class="hljs-title function_">throws</span>(throwingSecond, <span class="hljs-string">'Second'</span>);
<span class="hljs-comment">// TypeError [ERR_AMBIGUOUS_ARGUMENT]</span>
<span class="hljs-comment">// The string is only used (as message) in case the function does not throw:</span>
assert.<span class="hljs-title function_">throws</span>(notThrowing, <span class="hljs-string">'Second'</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: Missing expected exception: Second</span>
<span class="hljs-comment">// If it was intended to match for the error message do this instead:</span>
<span class="hljs-comment">// It does not throw because the error messages match.</span>
assert.<span class="hljs-title function_">throws</span>(throwingSecond, <span class="hljs-regexp">/Second$/</span>);
<span class="hljs-comment">// If the error message does not match, an AssertionError is thrown.</span>
assert.<span class="hljs-title function_">throws</span>(throwingFirst, <span class="hljs-regexp">/Second$/</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert/strict'</span>);
<span class="hljs-keyword">function</span> <span class="hljs-title function_">throwingFirst</span>(<span class="hljs-params"></span>) {
<span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'First'</span>);
}
<span class="hljs-keyword">function</span> <span class="hljs-title function_">throwingSecond</span>(<span class="hljs-params"></span>) {
<span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>(<span class="hljs-string">'Second'</span>);
}
<span class="hljs-keyword">function</span> <span class="hljs-title function_">notThrowing</span>(<span class="hljs-params"></span>) {}
<span class="hljs-comment">// The second argument is a string and the input function threw an Error.</span>
<span class="hljs-comment">// The first case will not throw as it does not match for the error message</span>
<span class="hljs-comment">// thrown by the input function!</span>
assert.<span class="hljs-title function_">throws</span>(throwingFirst, <span class="hljs-string">'Second'</span>);
<span class="hljs-comment">// In the next example the message has no benefit over the message from the</span>
<span class="hljs-comment">// error and since it is not clear if the user intended to actually match</span>
<span class="hljs-comment">// against the error message, Node.js throws an `ERR_AMBIGUOUS_ARGUMENT` error.</span>
assert.<span class="hljs-title function_">throws</span>(throwingSecond, <span class="hljs-string">'Second'</span>);
<span class="hljs-comment">// TypeError [ERR_AMBIGUOUS_ARGUMENT]</span>
<span class="hljs-comment">// The string is only used (as message) in case the function does not throw:</span>
assert.<span class="hljs-title function_">throws</span>(notThrowing, <span class="hljs-string">'Second'</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]: Missing expected exception: Second</span>
<span class="hljs-comment">// If it was intended to match for the error message do this instead:</span>
<span class="hljs-comment">// It does not throw because the error messages match.</span>
assert.<span class="hljs-title function_">throws</span>(throwingSecond, <span class="hljs-regexp">/Second$/</span>);
<span class="hljs-comment">// If the error message does not match, an AssertionError is thrown.</span>
assert.<span class="hljs-title function_">throws</span>(throwingFirst, <span class="hljs-regexp">/Second$/</span>);
<span class="hljs-comment">// AssertionError [ERR_ASSERTION]</span></code><button class="copy-button">copy</button></pre>
<p>Due to the confusing error-prone notation, avoid a string as the second
argument.</p></section>
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