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# Performance measurement APIs <!--introduced_in=v8.5.0--> > Stability: 2 - Stable <!-- source_link=lib/perf_hooks.js --> This module provides an implementation of a subset of the W3C [Web Performance APIs][] as well as additional APIs for Node.js-specific performance measurements. Node.js supports the following [Web Performance APIs][]: * [High Resolution Time][] * [Performance Timeline][] * [User Timing][] * [Resource Timing][] ```js const { PerformanceObserver, performance } = require('node:perf_hooks'); const obs = new PerformanceObserver((items) => { console.log(items.getEntries()[0].duration); performance.clearMarks(); }); obs.observe({ type: 'measure' }); performance.measure('Start to Now'); performance.mark('A'); doSomeLongRunningProcess(() => { performance.measure('A to Now', 'A'); performance.mark('B'); performance.measure('A to B', 'A', 'B'); }); ``` ## `perf_hooks.performance` <!-- YAML added: v8.5.0 --> An object that can be used to collect performance metrics from the current Node.js instance. It is similar to [`window.performance`][] in browsers. ### `performance.clearMarks([name])` <!-- YAML added: v8.5.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This method must be called with the `performance` object as the receiver. --> * `name` {string} If `name` is not provided, removes all `PerformanceMark` objects from the Performance Timeline. If `name` is provided, removes only the named mark. ### `performance.clearMeasures([name])` <!-- YAML added: v16.7.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This method must be called with the `performance` object as the receiver. --> * `name` {string} If `name` is not provided, removes all `PerformanceMeasure` objects from the Performance Timeline. If `name` is provided, removes only the named measure. ### `performance.clearResourceTimings([name])` <!-- YAML added: - v18.2.0 - v16.17.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This method must be called with the `performance` object as the receiver. --> * `name` {string} If `name` is not provided, removes all `PerformanceResourceTiming` objects from the Resource Timeline. If `name` is provided, removes only the named resource. ### `performance.eventLoopUtilization([utilization1[, utilization2]])` <!-- YAML added: - v14.10.0 - v12.19.0 --> * `utilization1` {Object} The result of a previous call to `eventLoopUtilization()`. * `utilization2` {Object} The result of a previous call to `eventLoopUtilization()` prior to `utilization1`. * Returns: {Object} * `idle` {number} * `active` {number} * `utilization` {number} The `eventLoopUtilization()` method returns an object that contains the cumulative duration of time the event loop has been both idle and active as a high resolution milliseconds timer. The `utilization` value is the calculated Event Loop Utilization (ELU). If bootstrapping has not yet finished on the main thread the properties have the value of `0`. The ELU is immediately available on [Worker threads][] since bootstrap happens within the event loop. Both `utilization1` and `utilization2` are optional parameters. If `utilization1` is passed, then the delta between the current call's `active` and `idle` times, as well as the corresponding `utilization` value are calculated and returned (similar to [`process.hrtime()`][]). If `utilization1` and `utilization2` are both passed, then the delta is calculated between the two arguments. This is a convenience option because, unlike [`process.hrtime()`][], calculating the ELU is more complex than a single subtraction. ELU is similar to CPU utilization, except that it only measures event loop statistics and not CPU usage. It represents the percentage of time the event loop has spent outside the event loop's event provider (e.g. `epoll_wait`). No other CPU idle time is taken into consideration. The following is an example of how a mostly idle process will have a high ELU. ```js 'use strict'; const { eventLoopUtilization } = require('node:perf_hooks').performance; const { spawnSync } = require('node:child_process'); setImmediate(() => { const elu = eventLoopUtilization(); spawnSync('sleep', ['5']); console.log(eventLoopUtilization(elu).utilization); }); ``` Although the CPU is mostly idle while running this script, the value of `utilization` is `1`. This is because the call to [`child_process.spawnSync()`][] blocks the event loop from proceeding. Passing in a user-defined object instead of the result of a previous call to `eventLoopUtilization()` will lead to undefined behavior. The return values are not guaranteed to reflect any correct state of the event loop. ### `performance.getEntries()` <!-- YAML added: v16.7.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This method must be called with the `performance` object as the receiver. --> * Returns: {PerformanceEntry\[]} Returns a list of `PerformanceEntry` objects in chronological order with respect to `performanceEntry.startTime`. If you are only interested in performance entries of certain types or that have certain names, see `performance.getEntriesByType()` and `performance.getEntriesByName()`. ### `performance.getEntriesByName(name[, type])` <!-- YAML added: v16.7.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This method must be called with the `performance` object as the receiver. --> * `name` {string} * `type` {string} * Returns: {PerformanceEntry\[]} Returns a list of `PerformanceEntry` objects in chronological order with respect to `performanceEntry.startTime` whose `performanceEntry.name` is equal to `name`, and optionally, whose `performanceEntry.entryType` is equal to `type`. ### `performance.getEntriesByType(type)` <!-- YAML added: v16.7.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This method must be called with the `performance` object as the receiver. --> * `type` {string} * Returns: {PerformanceEntry\[]} Returns a list of `PerformanceEntry` objects in chronological order with respect to `performanceEntry.startTime` whose `performanceEntry.entryType` is equal to `type`. ### `performance.mark(name[, options])` <!-- YAML added: v8.5.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This method must be called with the `performance` object as the receiver. The name argument is no longer optional. - version: v16.0.0 pr-url: https://github.com/nodejs/node/pull/37136 description: Updated to conform to the User Timing Level 3 specification. --> * `name` {string} * `options` {Object} * `detail` {any} Additional optional detail to include with the mark. * `startTime` {number} An optional timestamp to be used as the mark time. **Default**: `performance.now()`. Creates a new `PerformanceMark` entry in the Performance Timeline. A `PerformanceMark` is a subclass of `PerformanceEntry` whose `performanceEntry.entryType` is always `'mark'`, and whose `performanceEntry.duration` is always `0`. Performance marks are used to mark specific significant moments in the Performance Timeline. The created `PerformanceMark` entry is put in the global Performance Timeline and can be queried with `performance.getEntries`, `performance.getEntriesByName`, and `performance.getEntriesByType`. When the observation is performed, the entries should be cleared from the global Performance Timeline manually with `performance.clearMarks`. ### `performance.markResourceTiming(timingInfo, requestedUrl, initiatorType, global, cacheMode)` <!-- YAML added: - v18.2.0 - v16.17.0 --> * `timingInfo` {Object} [Fetch Timing Info][] * `requestedUrl` {string} The resource url * `initiatorType` {string} The initiator name, e.g: 'fetch' * `global` {Object} * `cacheMode` {string} The cache mode must be an empty string ('') or 'local' _This property is an extension by Node.js. It is not available in Web browsers._ Creates a new `PerformanceResourceTiming` entry in the Resource Timeline. A `PerformanceResourceTiming` is a subclass of `PerformanceEntry` whose `performanceEntry.entryType` is always `'resource'`. Performance resources are used to mark moments in the Resource Timeline. The created `PerformanceMark` entry is put in the global Resource Timeline and can be queried with `performance.getEntries`, `performance.getEntriesByName`, and `performance.getEntriesByType`. When the observation is performed, the entries should be cleared from the global Performance Timeline manually with `performance.clearResourceTimings`. ### `performance.measure(name[, startMarkOrOptions[, endMark]])` <!-- YAML added: v8.5.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This method must be called with the `performance` object as the receiver. - version: v16.0.0 pr-url: https://github.com/nodejs/node/pull/37136 description: Updated to conform to the User Timing Level 3 specification. - version: - v13.13.0 - v12.16.3 pr-url: https://github.com/nodejs/node/pull/32651 description: Make `startMark` and `endMark` parameters optional. --> * `name` {string} * `startMarkOrOptions` {string|Object} Optional. * `detail` {any} Additional optional detail to include with the measure. * `duration` {number} Duration between start and end times. * `end` {number|string} Timestamp to be used as the end time, or a string identifying a previously recorded mark. * `start` {number|string} Timestamp to be used as the start time, or a string identifying a previously recorded mark. * `endMark` {string} Optional. Must be omitted if `startMarkOrOptions` is an {Object}. Creates a new `PerformanceMeasure` entry in the Performance Timeline. A `PerformanceMeasure` is a subclass of `PerformanceEntry` whose `performanceEntry.entryType` is always `'measure'`, and whose `performanceEntry.duration` measures the number of milliseconds elapsed since `startMark` and `endMark`. The `startMark` argument may identify any _existing_ `PerformanceMark` in the Performance Timeline, or _may_ identify any of the timestamp properties provided by the `PerformanceNodeTiming` class. If the named `startMark` does not exist, an error is thrown. The optional `endMark` argument must identify any _existing_ `PerformanceMark` in the Performance Timeline or any of the timestamp properties provided by the `PerformanceNodeTiming` class. `endMark` will be `performance.now()` if no parameter is passed, otherwise if the named `endMark` does not exist, an error will be thrown. The created `PerformanceMeasure` entry is put in the global Performance Timeline and can be queried with `performance.getEntries`, `performance.getEntriesByName`, and `performance.getEntriesByType`. When the observation is performed, the entries should be cleared from the global Performance Timeline manually with `performance.clearMeasures`. ### `performance.nodeTiming` <!-- YAML added: v8.5.0 --> * {PerformanceNodeTiming} _This property is an extension by Node.js. It is not available in Web browsers._ An instance of the `PerformanceNodeTiming` class that provides performance metrics for specific Node.js operational milestones. ### `performance.now()` <!-- YAML added: v8.5.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This method must be called with the `performance` object as the receiver. --> * Returns: {number} Returns the current high resolution millisecond timestamp, where 0 represents the start of the current `node` process. ### `performance.setResourceTimingBufferSize(maxSize)` <!-- YAML added: v18.8.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This method must be called with the `performance` object as the receiver. --> Sets the global performance resource timing buffer size to the specified number of "resource" type performance entry objects. By default the max buffer size is set to 250. ### `performance.timeOrigin` <!-- YAML added: v8.5.0 --> * {number} The [`timeOrigin`][] specifies the high resolution millisecond timestamp at which the current `node` process began, measured in Unix time. ### `performance.timerify(fn[, options])` <!-- YAML added: v8.5.0 changes: - version: v16.0.0 pr-url: https://github.com/nodejs/node/pull/37475 description: Added the histogram option. - version: v16.0.0 pr-url: https://github.com/nodejs/node/pull/37136 description: Re-implemented to use pure-JavaScript and the ability to time async functions. --> * `fn` {Function} * `options` {Object} * `histogram` {RecordableHistogram} A histogram object created using `perf_hooks.createHistogram()` that will record runtime durations in nanoseconds. _This property is an extension by Node.js. It is not available in Web browsers._ Wraps a function within a new function that measures the running time of the wrapped function. A `PerformanceObserver` must be subscribed to the `'function'` event type in order for the timing details to be accessed. ```js const { performance, PerformanceObserver, } = require('node:perf_hooks'); function someFunction() { console.log('hello world'); } const wrapped = performance.timerify(someFunction); const obs = new PerformanceObserver((list) => { console.log(list.getEntries()[0].duration); performance.clearMarks(); performance.clearMeasures(); obs.disconnect(); }); obs.observe({ entryTypes: ['function'] }); // A performance timeline entry will be created wrapped(); ``` If the wrapped function returns a promise, a finally handler will be attached to the promise and the duration will be reported once the finally handler is invoked. ### `performance.toJSON()` <!-- YAML added: v16.1.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This method must be called with the `performance` object as the receiver. --> An object which is JSON representation of the `performance` object. It is similar to [`window.performance.toJSON`][] in browsers. #### Event: `'resourcetimingbufferfull'` <!-- YAML added: v18.8.0 --> The `'resourcetimingbufferfull'` event is fired when the global performance resource timing buffer is full. Adjust resource timing buffer size with `performance.setResourceTimingBufferSize()` or clear the buffer with `performance.clearResourceTimings()` in the event listener to allow more entries to be added to the performance timeline buffer. ## Class: `PerformanceEntry` <!-- YAML added: v8.5.0 --> The constructor of this class is not exposed to users directly. ### `performanceEntry.duration` <!-- YAML added: v8.5.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This property getter must be called with the `PerformanceEntry` object as the receiver. --> * {number} The total number of milliseconds elapsed for this entry. This value will not be meaningful for all Performance Entry types. ### `performanceEntry.entryType` <!-- YAML added: v8.5.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This property getter must be called with the `PerformanceEntry` object as the receiver. --> * {string} The type of the performance entry. It may be one of: * `'dns'` (Node.js only) * `'function'` (Node.js only) * `'gc'` (Node.js only) * `'http2'` (Node.js only) * `'http'` (Node.js only) * `'mark'` (available on the Web) * `'measure'` (available on the Web) * `'net'` (Node.js only) * `'node'` (Node.js only) * `'resource'` (available on the Web) ### `performanceEntry.name` <!-- YAML added: v8.5.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This property getter must be called with the `PerformanceEntry` object as the receiver. --> * {string} The name of the performance entry. ### `performanceEntry.startTime` <!-- YAML added: v8.5.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This property getter must be called with the `PerformanceEntry` object as the receiver. --> * {number} The high resolution millisecond timestamp marking the starting time of the Performance Entry. ## Class: `PerformanceMark` <!-- YAML added: - v18.2.0 - v16.17.0 --> * Extends: {PerformanceEntry} Exposes marks created via the `Performance.mark()` method. ### `performanceMark.detail` <!-- YAML added: v16.0.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This property getter must be called with the `PerformanceMark` object as the receiver. --> * {any} Additional detail specified when creating with `Performance.mark()` method. ## Class: `PerformanceMeasure` <!-- YAML added: - v18.2.0 - v16.17.0 --> * Extends: {PerformanceEntry} Exposes measures created via the `Performance.measure()` method. The constructor of this class is not exposed to users directly. ### `performanceMeasure.detail` <!-- YAML added: v16.0.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This property getter must be called with the `PerformanceMeasure` object as the receiver. --> * {any} Additional detail specified when creating with `Performance.measure()` method. ## Class: `PerformanceNodeEntry` <!-- YAML added: v19.0.0 --> * Extends: {PerformanceEntry} _This class is an extension by Node.js. It is not available in Web browsers._ Provides detailed Node.js timing data. The constructor of this class is not exposed to users directly. ### `performanceNodeEntry.detail` <!-- YAML added: v16.0.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This property getter must be called with the `PerformanceNodeEntry` object as the receiver. --> * {any} Additional detail specific to the `entryType`. ### `performanceNodeEntry.flags` <!-- YAML added: - v13.9.0 - v12.17.0 changes: - version: v16.0.0 pr-url: https://github.com/nodejs/node/pull/37136 description: Runtime deprecated. Now moved to the detail property when entryType is 'gc'. --> > Stability: 0 - Deprecated: Use `performanceNodeEntry.detail` instead. * {number} When `performanceEntry.entryType` is equal to `'gc'`, the `performance.flags` property contains additional information about garbage collection operation. The value may be one of: * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_NO` * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_CONSTRUCT_RETAINED` * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_FORCED` * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SYNCHRONOUS_PHANTOM_PROCESSING` * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_AVAILABLE_GARBAGE` * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_EXTERNAL_MEMORY` * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SCHEDULE_IDLE` ### `performanceNodeEntry.kind` <!-- YAML added: v8.5.0 changes: - version: v16.0.0 pr-url: https://github.com/nodejs/node/pull/37136 description: Runtime deprecated. Now moved to the detail property when entryType is 'gc'. --> > Stability: 0 - Deprecated: Use `performanceNodeEntry.detail` instead. * {number} When `performanceEntry.entryType` is equal to `'gc'`, the `performance.kind` property identifies the type of garbage collection operation that occurred. The value may be one of: * `perf_hooks.constants.NODE_PERFORMANCE_GC_MAJOR` * `perf_hooks.constants.NODE_PERFORMANCE_GC_MINOR` * `perf_hooks.constants.NODE_PERFORMANCE_GC_INCREMENTAL` * `perf_hooks.constants.NODE_PERFORMANCE_GC_WEAKCB` ### Garbage Collection ('gc') Details When `performanceEntry.type` is equal to `'gc'`, the `performanceNodeEntry.detail` property will be an {Object} with two properties: * `kind` {number} One of: * `perf_hooks.constants.NODE_PERFORMANCE_GC_MAJOR` * `perf_hooks.constants.NODE_PERFORMANCE_GC_MINOR` * `perf_hooks.constants.NODE_PERFORMANCE_GC_INCREMENTAL` * `perf_hooks.constants.NODE_PERFORMANCE_GC_WEAKCB` * `flags` {number} One of: * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_NO` * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_CONSTRUCT_RETAINED` * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_FORCED` * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SYNCHRONOUS_PHANTOM_PROCESSING` * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_AVAILABLE_GARBAGE` * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_EXTERNAL_MEMORY` * `perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SCHEDULE_IDLE` ### HTTP ('http') Details When `performanceEntry.type` is equal to `'http'`, the `performanceNodeEntry.detail` property will be an {Object} containing additional information. If `performanceEntry.name` is equal to `HttpClient`, the `detail` will contain the following properties: `req`, `res`. And the `req` property will be an {Object} containing `method`, `url`, `headers`, the `res` property will be an {Object} containing `statusCode`, `statusMessage`, `headers`. If `performanceEntry.name` is equal to `HttpRequest`, the `detail` will contain the following properties: `req`, `res`. And the `req` property will be an {Object} containing `method`, `url`, `headers`, the `res` property will be an {Object} containing `statusCode`, `statusMessage`, `headers`. This could add additional memory overhead and should only be used for diagnostic purposes, not left turned on in production by default. ### HTTP/2 ('http2') Details When `performanceEntry.type` is equal to `'http2'`, the `performanceNodeEntry.detail` property will be an {Object} containing additional performance information. If `performanceEntry.name` is equal to `Http2Stream`, the `detail` will contain the following properties: * `bytesRead` {number} The number of `DATA` frame bytes received for this `Http2Stream`. * `bytesWritten` {number} The number of `DATA` frame bytes sent for this `Http2Stream`. * `id` {number} The identifier of the associated `Http2Stream` * `timeToFirstByte` {number} The number of milliseconds elapsed between the `PerformanceEntry` `startTime` and the reception of the first `DATA` frame. * `timeToFirstByteSent` {number} The number of milliseconds elapsed between the `PerformanceEntry` `startTime` and sending of the first `DATA` frame. * `timeToFirstHeader` {number} The number of milliseconds elapsed between the `PerformanceEntry` `startTime` and the reception of the first header. If `performanceEntry.name` is equal to `Http2Session`, the `detail` will contain the following properties: * `bytesRead` {number} The number of bytes received for this `Http2Session`. * `bytesWritten` {number} The number of bytes sent for this `Http2Session`. * `framesReceived` {number} The number of HTTP/2 frames received by the `Http2Session`. * `framesSent` {number} The number of HTTP/2 frames sent by the `Http2Session`. * `maxConcurrentStreams` {number} The maximum number of streams concurrently open during the lifetime of the `Http2Session`. * `pingRTT` {number} The number of milliseconds elapsed since the transmission of a `PING` frame and the reception of its acknowledgment. Only present if a `PING` frame has been sent on the `Http2Session`. * `streamAverageDuration` {number} The average duration (in milliseconds) for all `Http2Stream` instances. * `streamCount` {number} The number of `Http2Stream` instances processed by the `Http2Session`. * `type` {string} Either `'server'` or `'client'` to identify the type of `Http2Session`. ### Timerify ('function') Details When `performanceEntry.type` is equal to `'function'`, the `performanceNodeEntry.detail` property will be an {Array} listing the input arguments to the timed function. ### Net ('net') Details When `performanceEntry.type` is equal to `'net'`, the `performanceNodeEntry.detail` property will be an {Object} containing additional information. If `performanceEntry.name` is equal to `connect`, the `detail` will contain the following properties: `host`, `port`. ### DNS ('dns') Details When `performanceEntry.type` is equal to `'dns'`, the `performanceNodeEntry.detail` property will be an {Object} containing additional information. If `performanceEntry.name` is equal to `lookup`, the `detail` will contain the following properties: `hostname`, `family`, `hints`, `verbatim`, `addresses`. If `performanceEntry.name` is equal to `lookupService`, the `detail` will contain the following properties: `host`, `port`, `hostname`, `service`. If `performanceEntry.name` is equal to `queryxxx` or `getHostByAddr`, the `detail` will contain the following properties: `host`, `ttl`, `result`. The value of `result` is same as the result of `queryxxx` or `getHostByAddr`. ## Class: `PerformanceNodeTiming` <!-- YAML added: v8.5.0 --> * Extends: {PerformanceEntry} _This property is an extension by Node.js. It is not available in Web browsers._ Provides timing details for Node.js itself. The constructor of this class is not exposed to users. ### `performanceNodeTiming.bootstrapComplete` <!-- YAML added: v8.5.0 --> * {number} The high resolution millisecond timestamp at which the Node.js process completed bootstrapping. If bootstrapping has not yet finished, the property has the value of -1. ### `performanceNodeTiming.environment` <!-- YAML added: v8.5.0 --> * {number} The high resolution millisecond timestamp at which the Node.js environment was initialized. ### `performanceNodeTiming.idleTime` <!-- YAML added: - v14.10.0 - v12.19.0 --> * {number} The high resolution millisecond timestamp of the amount of time the event loop has been idle within the event loop's event provider (e.g. `epoll_wait`). This does not take CPU usage into consideration. If the event loop has not yet started (e.g., in the first tick of the main script), the property has the value of 0. ### `performanceNodeTiming.loopExit` <!-- YAML added: v8.5.0 --> * {number} The high resolution millisecond timestamp at which the Node.js event loop exited. If the event loop has not yet exited, the property has the value of -1. It can only have a value of not -1 in a handler of the [`'exit'`][] event. ### `performanceNodeTiming.loopStart` <!-- YAML added: v8.5.0 --> * {number} The high resolution millisecond timestamp at which the Node.js event loop started. If the event loop has not yet started (e.g., in the first tick of the main script), the property has the value of -1. ### `performanceNodeTiming.nodeStart` <!-- YAML added: v8.5.0 --> * {number} The high resolution millisecond timestamp at which the Node.js process was initialized. ### `performanceNodeTiming.uvMetricsInfo` <!-- YAML added: v20.18.0 --> * Returns: {Object} * `loopCount` {number} Number of event loop iterations. * `events` {number} Number of events that have been processed by the event handler. * `eventsWaiting` {number} Number of events that were waiting to be processed when the event provider was called. This is a wrapper to the `uv_metrics_info` function. It returns the current set of event loop metrics. It is recommended to use this property inside a function whose execution was scheduled using `setImmediate` to avoid collecting metrics before finishing all operations scheduled during the current loop iteration. ```cjs const { performance } = require('node:perf_hooks'); setImmediate(() => { console.log(performance.nodeTiming.uvMetricsInfo); }); ``` ```mjs import { performance } from 'node:perf_hooks'; setImmediate(() => { console.log(performance.nodeTiming.uvMetricsInfo); }); ``` ### `performanceNodeTiming.v8Start` <!-- YAML added: v8.5.0 --> * {number} The high resolution millisecond timestamp at which the V8 platform was initialized. ## Class: `PerformanceResourceTiming` <!-- YAML added: - v18.2.0 - v16.17.0 --> * Extends: {PerformanceEntry} Provides detailed network timing data regarding the loading of an application's resources. The constructor of this class is not exposed to users directly. ### `performanceResourceTiming.workerStart` <!-- YAML added: - v18.2.0 - v16.17.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This property getter must be called with the `PerformanceResourceTiming` object as the receiver. --> * {number} The high resolution millisecond timestamp at immediately before dispatching the `fetch` request. If the resource is not intercepted by a worker the property will always return 0. ### `performanceResourceTiming.redirectStart` <!-- YAML added: - v18.2.0 - v16.17.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This property getter must be called with the `PerformanceResourceTiming` object as the receiver. --> * {number} The high resolution millisecond timestamp that represents the start time of the fetch which initiates the redirect. ### `performanceResourceTiming.redirectEnd` <!-- YAML added: - v18.2.0 - v16.17.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This property getter must be called with the `PerformanceResourceTiming` object as the receiver. --> * {number} The high resolution millisecond timestamp that will be created immediately after receiving the last byte of the response of the last redirect. ### `performanceResourceTiming.fetchStart` <!-- YAML added: - v18.2.0 - v16.17.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This property getter must be called with the `PerformanceResourceTiming` object as the receiver. --> * {number} The high resolution millisecond timestamp immediately before the Node.js starts to fetch the resource. ### `performanceResourceTiming.domainLookupStart` <!-- YAML added: - v18.2.0 - v16.17.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This property getter must be called with the `PerformanceResourceTiming` object as the receiver. --> * {number} The high resolution millisecond timestamp immediately before the Node.js starts the domain name lookup for the resource. ### `performanceResourceTiming.domainLookupEnd` <!-- YAML added: - v18.2.0 - v16.17.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This property getter must be called with the `PerformanceResourceTiming` object as the receiver. --> * {number} The high resolution millisecond timestamp representing the time immediately after the Node.js finished the domain name lookup for the resource. ### `performanceResourceTiming.connectStart` <!-- YAML added: - v18.2.0 - v16.17.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This property getter must be called with the `PerformanceResourceTiming` object as the receiver. --> * {number} The high resolution millisecond timestamp representing the time immediately before Node.js starts to establish the connection to the server to retrieve the resource. ### `performanceResourceTiming.connectEnd` <!-- YAML added: - v18.2.0 - v16.17.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This property getter must be called with the `PerformanceResourceTiming` object as the receiver. --> * {number} The high resolution millisecond timestamp representing the time immediately after Node.js finishes establishing the connection to the server to retrieve the resource. ### `performanceResourceTiming.secureConnectionStart` <!-- YAML added: - v18.2.0 - v16.17.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This property getter must be called with the `PerformanceResourceTiming` object as the receiver. --> * {number} The high resolution millisecond timestamp representing the time immediately before Node.js starts the handshake process to secure the current connection. ### `performanceResourceTiming.requestStart` <!-- YAML added: - v18.2.0 - v16.17.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This property getter must be called with the `PerformanceResourceTiming` object as the receiver. --> * {number} The high resolution millisecond timestamp representing the time immediately before Node.js receives the first byte of the response from the server. ### `performanceResourceTiming.responseEnd` <!-- YAML added: - v18.2.0 - v16.17.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This property getter must be called with the `PerformanceResourceTiming` object as the receiver. --> * {number} The high resolution millisecond timestamp representing the time immediately after Node.js receives the last byte of the resource or immediately before the transport connection is closed, whichever comes first. ### `performanceResourceTiming.transferSize` <!-- YAML added: - v18.2.0 - v16.17.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This property getter must be called with the `PerformanceResourceTiming` object as the receiver. --> * {number} A number representing the size (in octets) of the fetched resource. The size includes the response header fields plus the response payload body. ### `performanceResourceTiming.encodedBodySize` <!-- YAML added: - v18.2.0 - v16.17.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This property getter must be called with the `PerformanceResourceTiming` object as the receiver. --> * {number} A number representing the size (in octets) received from the fetch (HTTP or cache), of the payload body, before removing any applied content-codings. ### `performanceResourceTiming.decodedBodySize` <!-- YAML added: - v18.2.0 - v16.17.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This property getter must be called with the `PerformanceResourceTiming` object as the receiver. --> * {number} A number representing the size (in octets) received from the fetch (HTTP or cache), of the message body, after removing any applied content-codings. ### `performanceResourceTiming.toJSON()` <!-- YAML added: - v18.2.0 - v16.17.0 changes: - version: v19.0.0 pr-url: https://github.com/nodejs/node/pull/44483 description: This method must be called with the `PerformanceResourceTiming` object as the receiver. --> Returns a `object` that is the JSON representation of the `PerformanceResourceTiming` object ## Class: `PerformanceObserver` <!-- YAML added: v8.5.0 --> ### `PerformanceObserver.supportedEntryTypes` <!-- YAML added: v16.0.0 --> * {string\[]} Get supported types. ### `new PerformanceObserver(callback)` <!-- YAML added: v8.5.0 changes: - version: v18.0.0 pr-url: https://github.com/nodejs/node/pull/41678 description: Passing an invalid callback to the `callback` argument now throws `ERR_INVALID_ARG_TYPE` instead of `ERR_INVALID_CALLBACK`. --> * `callback` {Function} * `list` {PerformanceObserverEntryList} * `observer` {PerformanceObserver} `PerformanceObserver` objects provide notifications when new `PerformanceEntry` instances have been added to the Performance Timeline. ```js const { performance, PerformanceObserver, } = require('node:perf_hooks'); const obs = new PerformanceObserver((list, observer) => { console.log(list.getEntries()); performance.clearMarks(); performance.clearMeasures(); observer.disconnect(); }); obs.observe({ entryTypes: ['mark'], buffered: true }); performance.mark('test'); ``` Because `PerformanceObserver` instances introduce their own additional performance overhead, instances should not be left subscribed to notifications indefinitely. Users should disconnect observers as soon as they are no longer needed. The `callback` is invoked when a `PerformanceObserver` is notified about new `PerformanceEntry` instances. The callback receives a `PerformanceObserverEntryList` instance and a reference to the `PerformanceObserver`. ### `performanceObserver.disconnect()` <!-- YAML added: v8.5.0 --> Disconnects the `PerformanceObserver` instance from all notifications. ### `performanceObserver.observe(options)` <!-- YAML added: v8.5.0 changes: - version: v16.7.0 pr-url: https://github.com/nodejs/node/pull/39297 description: Updated to conform to Performance Timeline Level 2. The buffered option has been added back. - version: v16.0.0 pr-url: https://github.com/nodejs/node/pull/37136 description: Updated to conform to User Timing Level 3. The buffered option has been removed. --> * `options` {Object} * `type` {string} A single {PerformanceEntry} type. Must not be given if `entryTypes` is already specified. * `entryTypes` {string\[]} An array of strings identifying the types of {PerformanceEntry} instances the observer is interested in. If not provided an error will be thrown. * `buffered` {boolean} If true, the observer callback is called with a list global `PerformanceEntry` buffered entries. If false, only `PerformanceEntry`s created after the time point are sent to the observer callback. **Default:** `false`. Subscribes the {PerformanceObserver} instance to notifications of new {PerformanceEntry} instances identified either by `options.entryTypes` or `options.type`: ```js const { performance, PerformanceObserver, } = require('node:perf_hooks'); const obs = new PerformanceObserver((list, observer) => { // Called once asynchronously. `list` contains three items. }); obs.observe({ type: 'mark' }); for (let n = 0; n < 3; n++) performance.mark(`test${n}`); ``` ## Class: `PerformanceObserverEntryList` <!-- YAML added: v8.5.0 --> The `PerformanceObserverEntryList` class is used to provide access to the `PerformanceEntry` instances passed to a `PerformanceObserver`. The constructor of this class is not exposed to users. ### `performanceObserverEntryList.getEntries()` <!-- YAML added: v8.5.0 --> * Returns: {PerformanceEntry\[]} Returns a list of `PerformanceEntry` objects in chronological order with respect to `performanceEntry.startTime`. ```js const { performance, PerformanceObserver, } = require('node:perf_hooks'); const obs = new PerformanceObserver((perfObserverList, observer) => { console.log(perfObserverList.getEntries()); /** * [ * PerformanceEntry { * name: 'test', * entryType: 'mark', * startTime: 81.465639, * duration: 0, * detail: null * }, * PerformanceEntry { * name: 'meow', * entryType: 'mark', * startTime: 81.860064, * duration: 0, * detail: null * } * ] */ performance.clearMarks(); performance.clearMeasures(); observer.disconnect(); }); obs.observe({ type: 'mark' }); performance.mark('test'); performance.mark('meow'); ``` ### `performanceObserverEntryList.getEntriesByName(name[, type])` <!-- YAML added: v8.5.0 --> * `name` {string} * `type` {string} * Returns: {PerformanceEntry\[]} Returns a list of `PerformanceEntry` objects in chronological order with respect to `performanceEntry.startTime` whose `performanceEntry.name` is equal to `name`, and optionally, whose `performanceEntry.entryType` is equal to `type`. ```js const { performance, PerformanceObserver, } = require('node:perf_hooks'); const obs = new PerformanceObserver((perfObserverList, observer) => { console.log(perfObserverList.getEntriesByName('meow')); /** * [ * PerformanceEntry { * name: 'meow', * entryType: 'mark', * startTime: 98.545991, * duration: 0, * detail: null * } * ] */ console.log(perfObserverList.getEntriesByName('nope')); // [] console.log(perfObserverList.getEntriesByName('test', 'mark')); /** * [ * PerformanceEntry { * name: 'test', * entryType: 'mark', * startTime: 63.518931, * duration: 0, * detail: null * } * ] */ console.log(perfObserverList.getEntriesByName('test', 'measure')); // [] performance.clearMarks(); performance.clearMeasures(); observer.disconnect(); }); obs.observe({ entryTypes: ['mark', 'measure'] }); performance.mark('test'); performance.mark('meow'); ``` ### `performanceObserverEntryList.getEntriesByType(type)` <!-- YAML added: v8.5.0 --> * `type` {string} * Returns: {PerformanceEntry\[]} Returns a list of `PerformanceEntry` objects in chronological order with respect to `performanceEntry.startTime` whose `performanceEntry.entryType` is equal to `type`. ```js const { performance, PerformanceObserver, } = require('node:perf_hooks'); const obs = new PerformanceObserver((perfObserverList, observer) => { console.log(perfObserverList.getEntriesByType('mark')); /** * [ * PerformanceEntry { * name: 'test', * entryType: 'mark', * startTime: 55.897834, * duration: 0, * detail: null * }, * PerformanceEntry { * name: 'meow', * entryType: 'mark', * startTime: 56.350146, * duration: 0, * detail: null * } * ] */ performance.clearMarks(); performance.clearMeasures(); observer.disconnect(); }); obs.observe({ type: 'mark' }); performance.mark('test'); performance.mark('meow'); ``` ## `perf_hooks.createHistogram([options])` <!-- YAML added: - v15.9.0 - v14.18.0 --> * `options` {Object} * `lowest` {number|bigint} The lowest discernible value. Must be an integer value greater than 0. **Default:** `1`. * `highest` {number|bigint} The highest recordable value. Must be an integer value that is equal to or greater than two times `lowest`. **Default:** `Number.MAX_SAFE_INTEGER`. * `figures` {number} The number of accuracy digits. Must be a number between `1` and `5`. **Default:** `3`. * Returns: {RecordableHistogram} Returns a {RecordableHistogram}. ## `perf_hooks.monitorEventLoopDelay([options])` <!-- YAML added: v11.10.0 --> * `options` {Object} * `resolution` {number} The sampling rate in milliseconds. Must be greater than zero. **Default:** `10`. * Returns: {IntervalHistogram} _This property is an extension by Node.js. It is not available in Web browsers._ Creates an `IntervalHistogram` object that samples and reports the event loop delay over time. The delays will be reported in nanoseconds. Using a timer to detect approximate event loop delay works because the execution of timers is tied specifically to the lifecycle of the libuv event loop. That is, a delay in the loop will cause a delay in the execution of the timer, and those delays are specifically what this API is intended to detect. ```js const { monitorEventLoopDelay } = require('node:perf_hooks'); const h = monitorEventLoopDelay({ resolution: 20 }); h.enable(); // Do something. h.disable(); console.log(h.min); console.log(h.max); console.log(h.mean); console.log(h.stddev); console.log(h.percentiles); console.log(h.percentile(50)); console.log(h.percentile(99)); ``` ## Class: `Histogram` <!-- YAML added: v11.10.0 --> ### `histogram.count` <!-- YAML added: - v17.4.0 - v16.14.0 --> * {number} The number of samples recorded by the histogram. ### `histogram.countBigInt` <!-- YAML added: - v17.4.0 - v16.14.0 --> * {bigint} The number of samples recorded by the histogram. ### `histogram.exceeds` <!-- YAML added: v11.10.0 --> * {number} The number of times the event loop delay exceeded the maximum 1 hour event loop delay threshold. ### `histogram.exceedsBigInt` <!-- YAML added: - v17.4.0 - v16.14.0 --> * {bigint} The number of times the event loop delay exceeded the maximum 1 hour event loop delay threshold. ### `histogram.max` <!-- YAML added: v11.10.0 --> * {number} The maximum recorded event loop delay. ### `histogram.maxBigInt` <!-- YAML added: - v17.4.0 - v16.14.0 --> * {bigint} The maximum recorded event loop delay. ### `histogram.mean` <!-- YAML added: v11.10.0 --> * {number} The mean of the recorded event loop delays. ### `histogram.min` <!-- YAML added: v11.10.0 --> * {number} The minimum recorded event loop delay. ### `histogram.minBigInt` <!-- YAML added: - v17.4.0 - v16.14.0 --> * {bigint} The minimum recorded event loop delay. ### `histogram.percentile(percentile)` <!-- YAML added: v11.10.0 --> * `percentile` {number} A percentile value in the range (0, 100]. * Returns: {number} Returns the value at the given percentile. ### `histogram.percentileBigInt(percentile)` <!-- YAML added: - v17.4.0 - v16.14.0 --> * `percentile` {number} A percentile value in the range (0, 100]. * Returns: {bigint} Returns the value at the given percentile. ### `histogram.percentiles` <!-- YAML added: v11.10.0 --> * {Map} Returns a `Map` object detailing the accumulated percentile distribution. ### `histogram.percentilesBigInt` <!-- YAML added: - v17.4.0 - v16.14.0 --> * {Map} Returns a `Map` object detailing the accumulated percentile distribution. ### `histogram.reset()` <!-- YAML added: v11.10.0 --> Resets the collected histogram data. ### `histogram.stddev` <!-- YAML added: v11.10.0 --> * {number} The standard deviation of the recorded event loop delays. ## Class: `IntervalHistogram extends Histogram` A `Histogram` that is periodically updated on a given interval. ### `histogram.disable()` <!-- YAML added: v11.10.0 --> * Returns: {boolean} Disables the update interval timer. Returns `true` if the timer was stopped, `false` if it was already stopped. ### `histogram.enable()` <!-- YAML added: v11.10.0 --> * Returns: {boolean} Enables the update interval timer. Returns `true` if the timer was started, `false` if it was already started. ### Cloning an `IntervalHistogram` {IntervalHistogram} instances can be cloned via {MessagePort}. On the receiving end, the histogram is cloned as a plain {Histogram} object that does not implement the `enable()` and `disable()` methods. ## Class: `RecordableHistogram extends Histogram` <!-- YAML added: - v15.9.0 - v14.18.0 --> ### `histogram.add(other)` <!-- YAML added: - v17.4.0 - v16.14.0 --> * `other` {RecordableHistogram} Adds the values from `other` to this histogram. ### `histogram.record(val)` <!-- YAML added: - v15.9.0 - v14.18.0 --> * `val` {number|bigint} The amount to record in the histogram. ### `histogram.recordDelta()` <!-- YAML added: - v15.9.0 - v14.18.0 --> Calculates the amount of time (in nanoseconds) that has passed since the previous call to `recordDelta()` and records that amount in the histogram. ## Examples ### Measuring the duration of async operations The following example uses the [Async Hooks][] and Performance APIs to measure the actual duration of a Timeout operation (including the amount of time it took to execute the callback). ```js 'use strict'; const async_hooks = require('node:async_hooks'); const { performance, PerformanceObserver, } = require('node:perf_hooks'); const set = new Set(); const hook = async_hooks.createHook({ init(id, type) { if (type === 'Timeout') { performance.mark(`Timeout-${id}-Init`); set.add(id); } }, destroy(id) { if (set.has(id)) { set.delete(id); performance.mark(`Timeout-${id}-Destroy`); performance.measure(`Timeout-${id}`, `Timeout-${id}-Init`, `Timeout-${id}-Destroy`); } }, }); hook.enable(); const obs = new PerformanceObserver((list, observer) => { console.log(list.getEntries()[0]); performance.clearMarks(); performance.clearMeasures(); observer.disconnect(); }); obs.observe({ entryTypes: ['measure'], buffered: true }); setTimeout(() => {}, 1000); ``` ### Measuring how long it takes to load dependencies The following example measures the duration of `require()` operations to load dependencies: <!-- eslint-disable no-global-assign --> ```js 'use strict'; const { performance, PerformanceObserver, } = require('node:perf_hooks'); const mod = require('node:module'); // Monkey patch the require function mod.Module.prototype.require = performance.timerify(mod.Module.prototype.require); require = performance.timerify(require); // Activate the observer const obs = new PerformanceObserver((list) => { const entries = list.getEntries(); entries.forEach((entry) => { console.log(`require('${entry[0]}')`, entry.duration); }); performance.clearMarks(); performance.clearMeasures(); obs.disconnect(); }); obs.observe({ entryTypes: ['function'], buffered: true }); require('some-module'); ``` ### Measuring how long one HTTP round-trip takes The following example is used to trace the time spent by HTTP client (`OutgoingMessage`) and HTTP request (`IncomingMessage`). For HTTP client, it means the time interval between starting the request and receiving the response, and for HTTP request, it means the time interval between receiving the request and sending the response: ```js 'use strict'; const { PerformanceObserver } = require('node:perf_hooks'); const http = require('node:http'); const obs = new PerformanceObserver((items) => { items.getEntries().forEach((item) => { console.log(item); }); }); obs.observe({ entryTypes: ['http'] }); const PORT = 8080; http.createServer((req, res) => { res.end('ok'); }).listen(PORT, () => { http.get(`http://127.0.0.1:${PORT}`); }); ``` ### Measuring how long the `net.connect` (only for TCP) takes when the connection is successful ```js 'use strict'; const { PerformanceObserver } = require('node:perf_hooks'); const net = require('node:net'); const obs = new PerformanceObserver((items) => { items.getEntries().forEach((item) => { console.log(item); }); }); obs.observe({ entryTypes: ['net'] }); const PORT = 8080; net.createServer((socket) => { socket.destroy(); }).listen(PORT, () => { net.connect(PORT); }); ``` ### Measuring how long the DNS takes when the request is successful ```js 'use strict'; const { PerformanceObserver } = require('node:perf_hooks'); const dns = require('node:dns'); const obs = new PerformanceObserver((items) => { items.getEntries().forEach((item) => { console.log(item); }); }); obs.observe({ entryTypes: ['dns'] }); dns.lookup('localhost', () => {}); dns.promises.resolve('localhost'); ``` [Async Hooks]: async_hooks.md [Fetch Timing Info]: https://fetch.spec.whatwg.org/#fetch-timing-info [High Resolution Time]: https://www.w3.org/TR/hr-time-2 [Performance Timeline]: https://w3c.github.io/performance-timeline/ [Resource Timing]: https://www.w3.org/TR/resource-timing-2/ [User Timing]: https://www.w3.org/TR/user-timing/ [Web Performance APIs]: https://w3c.github.io/perf-timing-primer/ [Worker threads]: worker_threads.md#worker-threads [`'exit'`]: process.md#event-exit [`child_process.spawnSync()`]: child_process.md#child_processspawnsynccommand-args-options [`process.hrtime()`]: process.md#processhrtimetime [`timeOrigin`]: https://w3c.github.io/hr-time/#dom-performance-timeorigin [`window.performance.toJSON`]: https://developer.mozilla.org/en-US/docs/Web/API/Performance/toJSON [`window.performance`]: https://developer.mozilla.org/en-US/docs/Web/API/Window/performance