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/usr/share/doc/nodejs/api/perf_hooks.html
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<!doctype html> <html lang="en"> <head> <meta charset="utf-8"> <meta name="viewport" content="width=device-width"> <meta name="nodejs.org:node-version" content="v12.20.0"> <title>Performance measurement APIs | Node.js v12.20.0 Documentation</title> <link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Lato:400,700,400italic&display=fallback"> <link rel="stylesheet" href="assets/style.css"> <link rel="stylesheet" href="assets/hljs.css"> <link rel="canonical" href="https://nodejs.org/api/perf_hooks.html"> </head> <body class="alt apidoc" id="api-section-perf_hooks"> <div id="content" class="clearfix"> <div id="column2" class="interior"> <div id="intro" class="interior"> <a href="/" title="Go back to the home page"> Node.js </a> </div> <ul> <li><a href="documentation.html" class="nav-documentation">About this documentation</a></li> <li><a href="synopsis.html" class="nav-synopsis">Usage and example</a></li> </ul> <hr class="line"> <ul> <li><a href="assert.html" class="nav-assert">Assertion testing</a></li> <li><a href="async_hooks.html" class="nav-async_hooks">Async hooks</a></li> <li><a href="buffer.html" class="nav-buffer">Buffer</a></li> <li><a href="addons.html" class="nav-addons">C++ Addons</a></li> <li><a href="n-api.html" class="nav-n-api">C/C++ Addons with N-API</a></li> <li><a href="embedding.html" class="nav-embedding">C++ Embedder API</a></li> <li><a href="child_process.html" class="nav-child_process">Child Processes</a></li> <li><a href="cluster.html" class="nav-cluster">Cluster</a></li> <li><a href="cli.html" class="nav-cli">Command line options</a></li> <li><a href="console.html" class="nav-console">Console</a></li> <li><a href="crypto.html" class="nav-crypto">Crypto</a></li> <li><a href="debugger.html" class="nav-debugger">Debugger</a></li> <li><a href="deprecations.html" class="nav-deprecations">Deprecated APIs</a></li> <li><a href="dns.html" class="nav-dns">DNS</a></li> <li><a href="domain.html" class="nav-domain">Domain</a></li> <li><a href="errors.html" class="nav-errors">Errors</a></li> <li><a href="events.html" class="nav-events">Events</a></li> <li><a href="fs.html" class="nav-fs">File system</a></li> <li><a href="globals.html" class="nav-globals">Globals</a></li> <li><a href="http.html" class="nav-http">HTTP</a></li> <li><a href="http2.html" class="nav-http2">HTTP/2</a></li> <li><a href="https.html" class="nav-https">HTTPS</a></li> <li><a href="inspector.html" class="nav-inspector">Inspector</a></li> <li><a href="intl.html" class="nav-intl">Internationalization</a></li> <li><a href="modules.html" class="nav-modules">Modules: CommonJS modules</a></li> <li><a href="esm.html" class="nav-esm">Modules: ECMAScript modules</a></li> <li><a href="module.html" class="nav-module">Modules: <code>module</code> API</a></li> <li><a href="packages.html" class="nav-packages">Modules: Packages</a></li> <li><a href="net.html" class="nav-net">Net</a></li> <li><a href="os.html" class="nav-os">OS</a></li> <li><a href="path.html" class="nav-path">Path</a></li> <li><a href="perf_hooks.html" class="nav-perf_hooks active">Performance hooks</a></li> <li><a href="policy.html" class="nav-policy">Policies</a></li> <li><a href="process.html" class="nav-process">Process</a></li> <li><a href="punycode.html" class="nav-punycode">Punycode</a></li> <li><a href="querystring.html" class="nav-querystring">Query strings</a></li> <li><a href="readline.html" class="nav-readline">Readline</a></li> <li><a href="repl.html" class="nav-repl">REPL</a></li> <li><a href="report.html" class="nav-report">Report</a></li> <li><a href="stream.html" class="nav-stream">Stream</a></li> <li><a href="string_decoder.html" class="nav-string_decoder">String decoder</a></li> <li><a href="timers.html" class="nav-timers">Timers</a></li> <li><a href="tls.html" class="nav-tls">TLS/SSL</a></li> <li><a href="tracing.html" class="nav-tracing">Trace events</a></li> <li><a href="tty.html" class="nav-tty">TTY</a></li> <li><a href="dgram.html" class="nav-dgram">UDP/datagram</a></li> <li><a href="url.html" class="nav-url">URL</a></li> <li><a href="util.html" class="nav-util">Utilities</a></li> <li><a href="v8.html" class="nav-v8">V8</a></li> <li><a href="vm.html" class="nav-vm">VM</a></li> <li><a href="wasi.html" class="nav-wasi">WASI</a></li> <li><a href="worker_threads.html" class="nav-worker_threads">Worker threads</a></li> <li><a href="zlib.html" class="nav-zlib">Zlib</a></li> </ul> <hr class="line"> <ul> <li><a href="https://github.com/nodejs/node" class="nav-https-github-com-nodejs-node">Code repository and issue tracker</a></li> </ul> </div> <div id="column1" data-id="perf_hooks" class="interior"> <header> <h1>Node.js v12.20.0 Documentation</h1> <div id="gtoc"> <ul> <li> <a href="index.html">Index</a> </li> <li> <a href="all.html">View on single page</a> </li> <li> <a href="perf_hooks.json">View as JSON</a> </li> <li class="version-picker"> <a href="#">View another version <span>▼</span></a> <ol class="version-picker"><li><a href="https://nodejs.org/docs/latest-v15.x/api/perf_hooks.html">15.x</a></li> <li><a href="https://nodejs.org/docs/latest-v14.x/api/perf_hooks.html">14.x <b>LTS</b></a></li> <li><a href="https://nodejs.org/docs/latest-v13.x/api/perf_hooks.html">13.x</a></li> <li><a href="https://nodejs.org/docs/latest-v12.x/api/perf_hooks.html">12.x <b>LTS</b></a></li> <li><a href="https://nodejs.org/docs/latest-v11.x/api/perf_hooks.html">11.x</a></li> <li><a href="https://nodejs.org/docs/latest-v10.x/api/perf_hooks.html">10.x <b>LTS</b></a></li> <li><a href="https://nodejs.org/docs/latest-v9.x/api/perf_hooks.html">9.x</a></li> <li><a href="https://nodejs.org/docs/latest-v8.x/api/perf_hooks.html">8.x</a></li></ol> </li> <li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/master/doc/api/perf_hooks.md"><span class="github_icon"><svg height="16" width="16" viewBox="0 0 16.1 16.1" fill="currentColor"><path d="M8 0a8 8 0 0 0-2.5 15.6c.4 0 .5-.2.5-.4v-1.5c-2 .4-2.5-.5-2.7-1 0-.1-.5-.9-.8-1-.3-.2-.7-.6 0-.6.6 0 1 .6 1.2.8.7 1.2 1.9 1 2.4.7 0-.5.2-.9.5-1-1.8-.3-3.7-1-3.7-4 0-.9.3-1.6.8-2.2 0-.2-.3-1 .1-2 0 0 .7-.3 2.2.7a7.4 7.4 0 0 1 4 0c1.5-1 2.2-.8 2.2-.8.5 1.1.2 2 .1 2.1.5.6.8 1.3.8 2.2 0 3-1.9 3.7-3.6 4 .3.2.5.7.5 1.4v2.2c0 .2.1.5.5.4A8 8 0 0 0 16 8a8 8 0 0 0-8-8z"/></svg></span>Edit on GitHub</a></li> </ul> </div> <hr> </header> <div id="toc"> <h2>Table of Contents</h2> <ul> <li><span class="stability_2"><a href="#perf_hooks_performance_measurement_apis">Performance measurement APIs</a></span> <ul> <li><a href="#perf_hooks_perf_hooks_performance"><code>perf_hooks.performance</code></a> <ul> <li><a href="#perf_hooks_performance_clearmarks_name"><code>performance.clearMarks([name])</code></a></li> <li><a href="#perf_hooks_performance_mark_name"><code>performance.mark([name])</code></a></li> <li><a href="#perf_hooks_performance_measure_name_startmark_endmark"><code>performance.measure(name[, startMark[, endMark]])</code></a></li> <li><a href="#perf_hooks_performance_nodetiming"><code>performance.nodeTiming</code></a></li> <li><a href="#perf_hooks_performance_now"><code>performance.now()</code></a></li> <li><a href="#perf_hooks_performance_timeorigin"><code>performance.timeOrigin</code></a></li> <li><a href="#perf_hooks_performance_timerify_fn"><code>performance.timerify(fn)</code></a></li> <li><a href="#perf_hooks_performance_eventlooputilization_util1_util2"><code>performance.eventLoopUtilization([util1][,util2])</code></a></li> </ul> </li> <li><a href="#perf_hooks_class_performanceentry">Class: <code>PerformanceEntry</code></a> <ul> <li><a href="#perf_hooks_performanceentry_duration"><code>performanceEntry.duration</code></a></li> <li><a href="#perf_hooks_performanceentry_name"><code>performanceEntry.name</code></a></li> <li><a href="#perf_hooks_performanceentry_starttime"><code>performanceEntry.startTime</code></a></li> <li><a href="#perf_hooks_performanceentry_entrytype"><code>performanceEntry.entryType</code></a></li> <li><a href="#perf_hooks_performanceentry_kind"><code>performanceEntry.kind</code></a></li> <li><a href="#perf_hooks_performanceentry_flags">performanceEntry.flags</a></li> </ul> </li> <li><a href="#perf_hooks_class_performancenodetiming_extends_performanceentry">Class: <code>PerformanceNodeTiming extends PerformanceEntry</code></a> <ul> <li><a href="#perf_hooks_performancenodetiming_bootstrapcomplete"><code>performanceNodeTiming.bootstrapComplete</code></a></li> <li><a href="#perf_hooks_performancenodetiming_environment"><code>performanceNodeTiming.environment</code></a></li> <li><a href="#perf_hooks_performancenodetiming_loopexit"><code>performanceNodeTiming.loopExit</code></a></li> <li><a href="#perf_hooks_performancenodetiming_loopstart"><code>performanceNodeTiming.loopStart</code></a></li> <li><a href="#perf_hooks_performancenodetiming_nodestart"><code>performanceNodeTiming.nodeStart</code></a></li> <li><a href="#perf_hooks_performancenodetiming_v8start"><code>performanceNodeTiming.v8Start</code></a></li> <li><a href="#perf_hooks_performancenodetiming_idletime"><code>performanceNodeTiming.idleTime</code></a></li> </ul> </li> <li><a href="#perf_hooks_class_perf_hooks_performanceobserver">Class: <code>perf_hooks.PerformanceObserver</code></a> <ul> <li><a href="#perf_hooks_new_performanceobserver_callback"><code>new PerformanceObserver(callback)</code></a></li> <li><a href="#perf_hooks_performanceobserver_disconnect"><code>performanceObserver.disconnect()</code></a></li> <li><a href="#perf_hooks_performanceobserver_observe_options"><code>performanceObserver.observe(options)</code></a></li> </ul> </li> <li><a href="#perf_hooks_class_performanceobserverentrylist">Class: <code>PerformanceObserverEntryList</code></a> <ul> <li><a href="#perf_hooks_performanceobserverentrylist_getentries"><code>performanceObserverEntryList.getEntries()</code></a></li> <li><a href="#perf_hooks_performanceobserverentrylist_getentriesbyname_name_type"><code>performanceObserverEntryList.getEntriesByName(name[, type])</code></a></li> <li><a href="#perf_hooks_performanceobserverentrylist_getentriesbytype_type"><code>performanceObserverEntryList.getEntriesByType(type)</code></a></li> </ul> </li> <li><a href="#perf_hooks_perf_hooks_monitoreventloopdelay_options"><code>perf_hooks.monitorEventLoopDelay([options])</code></a> <ul> <li><a href="#perf_hooks_class_histogram">Class: <code>Histogram</code></a> <ul> <li><a href="#perf_hooks_histogram_disable"><code>histogram.disable()</code></a></li> <li><a href="#perf_hooks_histogram_enable"><code>histogram.enable()</code></a></li> <li><a href="#perf_hooks_histogram_exceeds"><code>histogram.exceeds</code></a></li> <li><a href="#perf_hooks_histogram_max"><code>histogram.max</code></a></li> <li><a href="#perf_hooks_histogram_mean"><code>histogram.mean</code></a></li> <li><a href="#perf_hooks_histogram_min"><code>histogram.min</code></a></li> <li><a href="#perf_hooks_histogram_percentile_percentile"><code>histogram.percentile(percentile)</code></a></li> <li><a href="#perf_hooks_histogram_percentiles"><code>histogram.percentiles</code></a></li> <li><a href="#perf_hooks_histogram_reset"><code>histogram.reset()</code></a></li> <li><a href="#perf_hooks_histogram_stddev"><code>histogram.stddev</code></a></li> </ul> </li> </ul> </li> <li><a href="#perf_hooks_examples">Examples</a> <ul> <li><a href="#perf_hooks_measuring_the_duration_of_async_operations">Measuring the duration of async operations</a></li> <li><a href="#perf_hooks_measuring_how_long_it_takes_to_load_dependencies">Measuring how long it takes to load dependencies</a></li> </ul> </li> </ul> </li> </ul> </div> <div id="apicontent"> <h1>Performance measurement APIs<span><a class="mark" href="#perf_hooks_performance_measurement_apis" id="perf_hooks_performance_measurement_apis">#</a></span></h1> <p></p><div class="api_stability api_stability_2"><a href="documentation.html#documentation_stability_index">Stability: 2</a> - Stable</div><p></p> <p><strong>Source Code:</strong> <a href="https://github.com/nodejs/node/blob/v12.20.0/lib/perf_hooks.js">lib/perf_hooks.js</a></p> <p>This module provides an implementation of a subset of the W3C <a href="https://w3c.github.io/perf-timing-primer/">Web Performance APIs</a> as well as additional APIs for Node.js-specific performance measurements.</p> <p>Node.js supports the following <a href="https://w3c.github.io/perf-timing-primer/">Web Performance APIs</a>:</p> <ul> <li><a href="https://www.w3.org/TR/hr-time-2">High Resolution Time</a></li> <li><a href="https://w3c.github.io/performance-timeline/">Performance Timeline</a></li> <li><a href="https://www.w3.org/TR/user-timing/">User Timing</a></li> </ul> <pre><code class="language-js"><span class="hljs-keyword">const</span> { PerformanceObserver, performance } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); <span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> PerformanceObserver(<span class="hljs-function">(<span class="hljs-params">items</span>) =></span> { <span class="hljs-built_in">console</span>.log(items.getEntries()[<span class="hljs-number">0</span>].duration); performance.clearMarks(); }); obs.observe({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'measure'</span>] }); performance.measure(<span class="hljs-string">'Start to Now'</span>); performance.mark(<span class="hljs-string">'A'</span>); doSomeLongRunningProcess(<span class="hljs-function">() =></span> { performance.measure(<span class="hljs-string">'A to Now'</span>, <span class="hljs-string">'A'</span>); performance.mark(<span class="hljs-string">'B'</span>); performance.measure(<span class="hljs-string">'A to B'</span>, <span class="hljs-string">'A'</span>, <span class="hljs-string">'B'</span>); });</code></pre> <h2><code>perf_hooks.performance</code><span><a class="mark" href="#perf_hooks_perf_hooks_performance" id="perf_hooks_perf_hooks_performance">#</a></span></h2> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <p>An object that can be used to collect performance metrics from the current Node.js instance. It is similar to <a href="https://developer.mozilla.org/en-US/docs/Web/API/Window/performance"><code>window.performance</code></a> in browsers.</p> <h3><code>performance.clearMarks([name])</code><span><a class="mark" href="#perf_hooks_performance_clearmarks_name" id="perf_hooks_performance_clearmarks_name">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> </ul> <p>If <code>name</code> is not provided, removes all <code>PerformanceMark</code> objects from the Performance Timeline. If <code>name</code> is provided, removes only the named mark.</p> <h3><code>performance.mark([name])</code><span><a class="mark" href="#perf_hooks_performance_mark_name" id="perf_hooks_performance_mark_name">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> </ul> <p>Creates a new <code>PerformanceMark</code> entry in the Performance Timeline. A <code>PerformanceMark</code> is a subclass of <code>PerformanceEntry</code> whose <code>performanceEntry.entryType</code> is always <code>'mark'</code>, and whose <code>performanceEntry.duration</code> is always <code>0</code>. Performance marks are used to mark specific significant moments in the Performance Timeline.</p> <h3><code>performance.measure(name[, startMark[, endMark]])</code><span><a class="mark" href="#perf_hooks_performance_measure_name_startmark_endmark" id="perf_hooks_performance_measure_name_startmark_endmark">#</a></span></h3> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v12.16.3</td> <td><p>Make <code>startMark</code> and <code>endMark</code> parameters optional.</p></td></tr> <tr><td>v8.5.0</td> <td><p><span>Added in: v8.5.0</span></p></td></tr> </tbody></table> </details> </div> <ul> <li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> <li><code>startMark</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Optional.</li> <li><code>endMark</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Optional.</li> </ul> <p>Creates a new <code>PerformanceMeasure</code> entry in the Performance Timeline. A <code>PerformanceMeasure</code> is a subclass of <code>PerformanceEntry</code> whose <code>performanceEntry.entryType</code> is always <code>'measure'</code>, and whose <code>performanceEntry.duration</code> measures the number of milliseconds elapsed since <code>startMark</code> and <code>endMark</code>.</p> <p>The <code>startMark</code> argument may identify any <em>existing</em> <code>PerformanceMark</code> in the Performance Timeline, or <em>may</em> identify any of the timestamp properties provided by the <code>PerformanceNodeTiming</code> class. If the named <code>startMark</code> does not exist, then <code>startMark</code> is set to <a href="https://w3c.github.io/hr-time/#dom-performance-timeorigin"><code>timeOrigin</code></a> by default.</p> <p>The optional <code>endMark</code> argument must identify any <em>existing</em> <code>PerformanceMark</code> in the Performance Timeline or any of the timestamp properties provided by the <code>PerformanceNodeTiming</code> class. <code>endMark</code> will be <code>performance.now()</code> if no parameter is passed, otherwise if the named <code>endMark</code> does not exist, an error will be thrown.</p> <h3><code>performance.nodeTiming</code><span><a class="mark" href="#perf_hooks_performance_nodetiming" id="perf_hooks_performance_nodetiming">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><a href="perf_hooks.html#perf_hooks_class_performancenodetiming_extends_performanceentry" class="type"><PerformanceNodeTiming></a></li> </ul> <p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> <p>An instance of the <code>PerformanceNodeTiming</code> class that provides performance metrics for specific Node.js operational milestones.</p> <h3><code>performance.now()</code><span><a class="mark" href="#perf_hooks_performance_now" id="perf_hooks_performance_now">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>Returns the current high resolution millisecond timestamp, where 0 represents the start of the current <code>node</code> process.</p> <h3><code>performance.timeOrigin</code><span><a class="mark" href="#perf_hooks_performance_timeorigin" id="perf_hooks_performance_timeorigin">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The <a href="https://w3c.github.io/hr-time/#dom-performance-timeorigin"><code>timeOrigin</code></a> specifies the high resolution millisecond timestamp at which the current <code>node</code> process began, measured in Unix time.</p> <h3><code>performance.timerify(fn)</code><span><a class="mark" href="#perf_hooks_performance_timerify_fn" id="perf_hooks_performance_timerify_fn">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.5.0</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></li> </ul> <p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> <p>Wraps a function within a new function that measures the running time of the wrapped function. A <code>PerformanceObserver</code> must be subscribed to the <code>'function'</code> event type in order for the timing details to be accessed.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> { performance, PerformanceObserver } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); <span class="hljs-function"><span class="hljs-keyword">function</span> <span class="hljs-title">someFunction</span>(<span class="hljs-params"></span>) </span>{ <span class="hljs-built_in">console</span>.log(<span class="hljs-string">'hello world'</span>); } <span class="hljs-keyword">const</span> wrapped = performance.timerify(someFunction); <span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> PerformanceObserver(<span class="hljs-function">(<span class="hljs-params">list</span>) =></span> { <span class="hljs-built_in">console</span>.log(list.getEntries()[<span class="hljs-number">0</span>].duration); obs.disconnect(); }); obs.observe({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'function'</span>] }); <span class="hljs-comment">// A performance timeline entry will be created</span> wrapped();</code></pre> <h3><code>performance.eventLoopUtilization([util1][,util2])</code><span><a class="mark" href="#perf_hooks_performance_eventlooputilization_util1_util2" id="perf_hooks_performance_eventlooputilization_util1_util2">#</a></span></h3> <div class="api_metadata"> <span>Added in: v12.19.0</span> </div> <ul> <li><code>util1</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> The result of a previous call to <code>eventLoopUtilization()</code></li> <li><code>util2</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> The result of a previous call to <code>eventLoopUtilization()</code> prior to <code>util1</code></li> <li>Returns <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> <ul> <li><code>idle</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> <li><code>active</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> <li><code>utilization</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> </li> </ul> <p>The <code>eventLoopUtilization()</code> 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 <code>utilization</code> value is the calculated Event Loop Utilization (ELU). If bootstrapping has not yet finished, the properties have the value of 0.</p> <p><code>util1</code> and <code>util2</code> are optional parameters.</p> <p>If <code>util1</code> is passed then the delta between the current call's <code>active</code> and <code>idle</code> times are calculated and returned (similar to <a href="process.html#process_process_hrtime_time"><code>process.hrtime()</code></a>). Likewise the adjusted <code>utilization</code> value is calculated.</p> <p>If <code>util1</code> and <code>util2</code> are both passed then the calculation adjustments are done between the two arguments. This is a convenience option because unlike <a href="process.html#process_process_hrtime_time"><code>process.hrtime()</code></a> additional work is done to calculate the ELU.</p> <p>ELU is similar to CPU utilization except that it is calculated using high precision wall-clock time. It represents the percentage of time the event loop has spent outside the event loop's event provider (e.g. <code>epoll_wait</code>). 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.</p> <!-- eslint-skip --> <pre><code class="language-js"><span class="hljs-meta">'use strict'</span>; <span class="hljs-keyword">const</span> { eventLoopUtilization } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>).performance; <span class="hljs-keyword">const</span> { spawnSync } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'child_process'</span>); setImmediate(<span class="hljs-function">() =></span> { <span class="hljs-keyword">const</span> elu = eventLoopUtilization(); spawnSync(<span class="hljs-string">'sleep'</span>, [<span class="hljs-string">'5'</span>]); <span class="hljs-built_in">console</span>.log(eventLoopUtilization(elu).utilization); });</code></pre> <p>Although the CPU is mostly idle while running this script, the value of <code>utilization</code> is 1. This is because the call to <a href="child_process.html#child_process_child_process_spawnsync_command_args_options"><code>child_process.spawnSync()</code></a> blocks the event loop from proceeding.</p> <p>Passing in a user-defined object instead of the result of a previous call to <code>eventLoopUtilization()</code> will lead to undefined behavior. The return values are not guaranteed to reflect any correct state of the event loop.</p> <h2>Class: <code>PerformanceEntry</code><span><a class="mark" href="#perf_hooks_class_performanceentry" id="perf_hooks_class_performanceentry">#</a></span></h2> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <h3><code>performanceEntry.duration</code><span><a class="mark" href="#perf_hooks_performanceentry_duration" id="perf_hooks_performanceentry_duration">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The total number of milliseconds elapsed for this entry. This value will not be meaningful for all Performance Entry types.</p> <h3><code>performanceEntry.name</code><span><a class="mark" href="#perf_hooks_performanceentry_name" id="perf_hooks_performanceentry_name">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> </ul> <p>The name of the performance entry.</p> <h3><code>performanceEntry.startTime</code><span><a class="mark" href="#perf_hooks_performanceentry_starttime" id="perf_hooks_performanceentry_starttime">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The high resolution millisecond timestamp marking the starting time of the Performance Entry.</p> <h3><code>performanceEntry.entryType</code><span><a class="mark" href="#perf_hooks_performanceentry_entrytype" id="perf_hooks_performanceentry_entrytype">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> </ul> <p>The type of the performance entry. It may be one of:</p> <ul> <li><code>'node'</code> (Node.js only)</li> <li><code>'mark'</code> (available on the Web)</li> <li><code>'measure'</code> (available on the Web)</li> <li><code>'gc'</code> (Node.js only)</li> <li><code>'function'</code> (Node.js only)</li> <li><code>'http2'</code> (Node.js only)</li> <li><code>'http'</code> (Node.js only)</li> </ul> <h3><code>performanceEntry.kind</code><span><a class="mark" href="#perf_hooks_performanceentry_kind" id="perf_hooks_performanceentry_kind">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> <p>When <code>performanceEntry.entryType</code> is equal to <code>'gc'</code>, the <code>performance.kind</code> property identifies the type of garbage collection operation that occurred. The value may be one of:</p> <ul> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_MAJOR</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_MINOR</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_INCREMENTAL</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_WEAKCB</code></li> </ul> <h3>performanceEntry.flags<span><a class="mark" href="#perf_hooks_performanceentry_flags" id="perf_hooks_performanceentry_flags">#</a></span></h3> <div class="api_metadata"> <span>Added in: v12.17.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> <p>When <code>performanceEntry.entryType</code> is equal to <code>'gc'</code>, the <code>performance.flags</code> property contains additional information about garbage collection operation. The value may be one of:</p> <ul> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_NO</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_CONSTRUCT_RETAINED</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_FORCED</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SYNCHRONOUS_PHANTOM_PROCESSING</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_AVAILABLE_GARBAGE</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_EXTERNAL_MEMORY</code></li> <li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SCHEDULE_IDLE</code></li> </ul> <h2>Class: <code>PerformanceNodeTiming extends PerformanceEntry</code><span><a class="mark" href="#perf_hooks_class_performancenodetiming_extends_performanceentry" id="perf_hooks_class_performancenodetiming_extends_performanceentry">#</a></span></h2> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> <p>Provides timing details for Node.js itself. The constructor of this class is not exposed to users.</p> <h3><code>performanceNodeTiming.bootstrapComplete</code><span><a class="mark" href="#perf_hooks_performancenodetiming_bootstrapcomplete" id="perf_hooks_performancenodetiming_bootstrapcomplete">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>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.</p> <h3><code>performanceNodeTiming.environment</code><span><a class="mark" href="#perf_hooks_performancenodetiming_environment" id="perf_hooks_performancenodetiming_environment">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The high resolution millisecond timestamp at which the Node.js environment was initialized.</p> <h3><code>performanceNodeTiming.loopExit</code><span><a class="mark" href="#perf_hooks_performancenodetiming_loopexit" id="perf_hooks_performancenodetiming_loopexit">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>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 <a href="process.html#process_event_exit"><code>'exit'</code></a> event.</p> <h3><code>performanceNodeTiming.loopStart</code><span><a class="mark" href="#perf_hooks_performancenodetiming_loopstart" id="perf_hooks_performancenodetiming_loopstart">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>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.</p> <h3><code>performanceNodeTiming.nodeStart</code><span><a class="mark" href="#perf_hooks_performancenodetiming_nodestart" id="perf_hooks_performancenodetiming_nodestart">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The high resolution millisecond timestamp at which the Node.js process was initialized.</p> <h3><code>performanceNodeTiming.v8Start</code><span><a class="mark" href="#perf_hooks_performancenodetiming_v8start" id="perf_hooks_performancenodetiming_v8start">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The high resolution millisecond timestamp at which the V8 platform was initialized.</p> <h3><code>performanceNodeTiming.idleTime</code><span><a class="mark" href="#perf_hooks_performancenodetiming_idletime" id="perf_hooks_performancenodetiming_idletime">#</a></span></h3> <div class="api_metadata"> <span>Added in: v12.19.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>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. <code>epoll_wait</code>). 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.</p> <h2>Class: <code>perf_hooks.PerformanceObserver</code><span><a class="mark" href="#perf_hooks_class_perf_hooks_performanceobserver" id="perf_hooks_class_perf_hooks_performanceobserver">#</a></span></h2> <h3><code>new PerformanceObserver(callback)</code><span><a class="mark" href="#perf_hooks_new_performanceobserver_callback" id="perf_hooks_new_performanceobserver_callback">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> <ul> <li><code>list</code> <a href="perf_hooks.html#perf_hooks_class_performanceobserverentrylist" class="type"><PerformanceObserverEntryList></a></li> <li><code>observer</code> <a href="perf_hooks.html#perf_hooks_class_perf_hooks_performanceobserver" class="type"><PerformanceObserver></a></li> </ul> </li> </ul> <p><code>PerformanceObserver</code> objects provide notifications when new <code>PerformanceEntry</code> instances have been added to the Performance Timeline.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> { performance, PerformanceObserver } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); <span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> PerformanceObserver(<span class="hljs-function">(<span class="hljs-params">list, observer</span>) =></span> { <span class="hljs-built_in">console</span>.log(list.getEntries()); observer.disconnect(); }); obs.observe({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'mark'</span>], <span class="hljs-attr">buffered</span>: <span class="hljs-literal">true</span> }); performance.mark(<span class="hljs-string">'test'</span>);</code></pre> <p>Because <code>PerformanceObserver</code> 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.</p> <p>The <code>callback</code> is invoked when a <code>PerformanceObserver</code> is notified about new <code>PerformanceEntry</code> instances. The callback receives a <code>PerformanceObserverEntryList</code> instance and a reference to the <code>PerformanceObserver</code>.</p> <h3><code>performanceObserver.disconnect()</code><span><a class="mark" href="#perf_hooks_performanceobserver_disconnect" id="perf_hooks_performanceobserver_disconnect">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <p>Disconnects the <code>PerformanceObserver</code> instance from all notifications.</p> <h3><code>performanceObserver.observe(options)</code><span><a class="mark" href="#perf_hooks_performanceobserver_observe_options" id="perf_hooks_performanceobserver_observe_options">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.5.0</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>entryTypes</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string[]></a> An array of strings identifying the types of <code>PerformanceEntry</code> instances the observer is interested in. If not provided an error will be thrown.</li> <li><code>buffered</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If true, the notification callback will be called using <code>setImmediate()</code> and multiple <code>PerformanceEntry</code> instance notifications will be buffered internally. If <code>false</code>, notifications will be immediate and synchronous. <strong>Default:</strong> <code>false</code>.</li> </ul> </li> </ul> <p>Subscribes the <code>PerformanceObserver</code> instance to notifications of new <code>PerformanceEntry</code> instances identified by <code>options.entryTypes</code>.</p> <p>When <code>options.buffered</code> is <code>false</code>, the <code>callback</code> will be invoked once for every <code>PerformanceEntry</code> instance:</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> { performance, PerformanceObserver } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); <span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> PerformanceObserver(<span class="hljs-function">(<span class="hljs-params">list, observer</span>) =></span> { <span class="hljs-comment">// Called three times synchronously. `list` contains one item.</span> }); obs.observe({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'mark'</span>] }); <span class="hljs-keyword">for</span> (<span class="hljs-keyword">let</span> n = <span class="hljs-number">0</span>; n < <span class="hljs-number">3</span>; n++) performance.mark(<span class="hljs-string">`test<span class="hljs-subst">${n}</span>`</span>);</code></pre> <pre><code class="language-js"><span class="hljs-keyword">const</span> { performance, PerformanceObserver } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); <span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> PerformanceObserver(<span class="hljs-function">(<span class="hljs-params">list, observer</span>) =></span> { <span class="hljs-comment">// Called once. `list` contains three items.</span> }); obs.observe({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'mark'</span>], <span class="hljs-attr">buffered</span>: <span class="hljs-literal">true</span> }); <span class="hljs-keyword">for</span> (<span class="hljs-keyword">let</span> n = <span class="hljs-number">0</span>; n < <span class="hljs-number">3</span>; n++) performance.mark(<span class="hljs-string">`test<span class="hljs-subst">${n}</span>`</span>);</code></pre> <h2>Class: <code>PerformanceObserverEntryList</code><span><a class="mark" href="#perf_hooks_class_performanceobserverentrylist" id="perf_hooks_class_performanceobserverentrylist">#</a></span></h2> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <p>The <code>PerformanceObserverEntryList</code> class is used to provide access to the <code>PerformanceEntry</code> instances passed to a <code>PerformanceObserver</code>. The constructor of this class is not exposed to users.</p> <h3><code>performanceObserverEntryList.getEntries()</code><span><a class="mark" href="#perf_hooks_performanceobserverentrylist_getentries" id="perf_hooks_performanceobserverentrylist_getentries">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li>Returns: <a href="perf_hooks.html#perf_hooks_class_performanceentry" class="type"><PerformanceEntry[]></a></li> </ul> <p>Returns a list of <code>PerformanceEntry</code> objects in chronological order with respect to <code>performanceEntry.startTime</code>.</p> <h3><code>performanceObserverEntryList.getEntriesByName(name[, type])</code><span><a class="mark" href="#perf_hooks_performanceobserverentrylist_getentriesbyname_name_type" id="perf_hooks_performanceobserverentrylist_getentriesbyname_name_type">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> <li><code>type</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> <li>Returns: <a href="perf_hooks.html#perf_hooks_class_performanceentry" class="type"><PerformanceEntry[]></a></li> </ul> <p>Returns a list of <code>PerformanceEntry</code> objects in chronological order with respect to <code>performanceEntry.startTime</code> whose <code>performanceEntry.name</code> is equal to <code>name</code>, and optionally, whose <code>performanceEntry.entryType</code> is equal to <code>type</code>.</p> <h3><code>performanceObserverEntryList.getEntriesByType(type)</code><span><a class="mark" href="#perf_hooks_performanceobserverentrylist_getentriesbytype_type" id="perf_hooks_performanceobserverentrylist_getentriesbytype_type">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.5.0</span> </div> <ul> <li><code>type</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> <li>Returns: <a href="perf_hooks.html#perf_hooks_class_performanceentry" class="type"><PerformanceEntry[]></a></li> </ul> <p>Returns a list of <code>PerformanceEntry</code> objects in chronological order with respect to <code>performanceEntry.startTime</code> whose <code>performanceEntry.entryType</code> is equal to <code>type</code>.</p> <h2><code>perf_hooks.monitorEventLoopDelay([options])</code><span><a class="mark" href="#perf_hooks_perf_hooks_monitoreventloopdelay_options" id="perf_hooks_perf_hooks_monitoreventloopdelay_options">#</a></span></h2> <div class="api_metadata"> <span>Added in: v11.10.0</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>resolution</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The sampling rate in milliseconds. Must be greater than zero. <strong>Default:</strong> <code>10</code>.</li> </ul> </li> <li>Returns: <a href="perf_hooks.html#perf_hooks_class_histogram" class="type"><Histogram></a></li> </ul> <p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> <p>Creates a <code>Histogram</code> object that samples and reports the event loop delay over time. The delays will be reported in nanoseconds.</p> <p>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.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> { monitorEventLoopDelay } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); <span class="hljs-keyword">const</span> h = monitorEventLoopDelay({ <span class="hljs-attr">resolution</span>: <span class="hljs-number">20</span> }); h.enable(); <span class="hljs-comment">// Do something.</span> h.disable(); <span class="hljs-built_in">console</span>.log(h.min); <span class="hljs-built_in">console</span>.log(h.max); <span class="hljs-built_in">console</span>.log(h.mean); <span class="hljs-built_in">console</span>.log(h.stddev); <span class="hljs-built_in">console</span>.log(h.percentiles); <span class="hljs-built_in">console</span>.log(h.percentile(<span class="hljs-number">50</span>)); <span class="hljs-built_in">console</span>.log(h.percentile(<span class="hljs-number">99</span>));</code></pre> <h3>Class: <code>Histogram</code><span><a class="mark" href="#perf_hooks_class_histogram" id="perf_hooks_class_histogram">#</a></span></h3> <div class="api_metadata"> <span>Added in: v11.10.0</span> </div> <p>Tracks the event loop delay at a given sampling rate. The constructor of this class not exposed to users.</p> <p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> <h4><code>histogram.disable()</code><span><a class="mark" href="#perf_hooks_histogram_disable" id="perf_hooks_histogram_disable">#</a></span></h4> <div class="api_metadata"> <span>Added in: v11.10.0</span> </div> <ul> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Disables the event loop delay sample timer. Returns <code>true</code> if the timer was stopped, <code>false</code> if it was already stopped.</p> <h4><code>histogram.enable()</code><span><a class="mark" href="#perf_hooks_histogram_enable" id="perf_hooks_histogram_enable">#</a></span></h4> <div class="api_metadata"> <span>Added in: v11.10.0</span> </div> <ul> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> </ul> <p>Enables the event loop delay sample timer. Returns <code>true</code> if the timer was started, <code>false</code> if it was already started.</p> <h4><code>histogram.exceeds</code><span><a class="mark" href="#perf_hooks_histogram_exceeds" id="perf_hooks_histogram_exceeds">#</a></span></h4> <div class="api_metadata"> <span>Added in: v11.10.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The number of times the event loop delay exceeded the maximum 1 hour event loop delay threshold.</p> <h4><code>histogram.max</code><span><a class="mark" href="#perf_hooks_histogram_max" id="perf_hooks_histogram_max">#</a></span></h4> <div class="api_metadata"> <span>Added in: v11.10.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The maximum recorded event loop delay.</p> <h4><code>histogram.mean</code><span><a class="mark" href="#perf_hooks_histogram_mean" id="perf_hooks_histogram_mean">#</a></span></h4> <div class="api_metadata"> <span>Added in: v11.10.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The mean of the recorded event loop delays.</p> <h4><code>histogram.min</code><span><a class="mark" href="#perf_hooks_histogram_min" id="perf_hooks_histogram_min">#</a></span></h4> <div class="api_metadata"> <span>Added in: v11.10.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The minimum recorded event loop delay.</p> <h4><code>histogram.percentile(percentile)</code><span><a class="mark" href="#perf_hooks_histogram_percentile_percentile" id="perf_hooks_histogram_percentile_percentile">#</a></span></h4> <div class="api_metadata"> <span>Added in: v11.10.0</span> </div> <ul> <li><code>percentile</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> A percentile value between 1 and 100.</li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>Returns the value at the given percentile.</p> <h4><code>histogram.percentiles</code><span><a class="mark" href="#perf_hooks_histogram_percentiles" id="perf_hooks_histogram_percentiles">#</a></span></h4> <div class="api_metadata"> <span>Added in: v11.10.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map" class="type"><Map></a></li> </ul> <p>Returns a <code>Map</code> object detailing the accumulated percentile distribution.</p> <h4><code>histogram.reset()</code><span><a class="mark" href="#perf_hooks_histogram_reset" id="perf_hooks_histogram_reset">#</a></span></h4> <div class="api_metadata"> <span>Added in: v11.10.0</span> </div> <p>Resets the collected histogram data.</p> <h4><code>histogram.stddev</code><span><a class="mark" href="#perf_hooks_histogram_stddev" id="perf_hooks_histogram_stddev">#</a></span></h4> <div class="api_metadata"> <span>Added in: v11.10.0</span> </div> <ul> <li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> </ul> <p>The standard deviation of the recorded event loop delays.</p> <h2>Examples<span><a class="mark" href="#perf_hooks_examples" id="perf_hooks_examples">#</a></span></h2> <h3>Measuring the duration of async operations<span><a class="mark" href="#perf_hooks_measuring_the_duration_of_async_operations" id="perf_hooks_measuring_the_duration_of_async_operations">#</a></span></h3> <p>The following example uses the <a href="async_hooks.html">Async Hooks</a> and Performance APIs to measure the actual duration of a Timeout operation (including the amount of time it took to execute the callback).</p> <pre><code class="language-js"><span class="hljs-meta">'use strict'</span>; <span class="hljs-keyword">const</span> async_hooks = <span class="hljs-built_in">require</span>(<span class="hljs-string">'async_hooks'</span>); <span class="hljs-keyword">const</span> { performance, PerformanceObserver } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); <span class="hljs-keyword">const</span> set = <span class="hljs-keyword">new</span> <span class="hljs-built_in">Set</span>(); <span class="hljs-keyword">const</span> hook = async_hooks.createHook({ init(id, type) { <span class="hljs-keyword">if</span> (type === <span class="hljs-string">'Timeout'</span>) { performance.mark(<span class="hljs-string">`Timeout-<span class="hljs-subst">${id}</span>-Init`</span>); set.add(id); } }, destroy(id) { <span class="hljs-keyword">if</span> (set.has(id)) { set.delete(id); performance.mark(<span class="hljs-string">`Timeout-<span class="hljs-subst">${id}</span>-Destroy`</span>); performance.measure(<span class="hljs-string">`Timeout-<span class="hljs-subst">${id}</span>`</span>, <span class="hljs-string">`Timeout-<span class="hljs-subst">${id}</span>-Init`</span>, <span class="hljs-string">`Timeout-<span class="hljs-subst">${id}</span>-Destroy`</span>); } } }); hook.enable(); <span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> PerformanceObserver(<span class="hljs-function">(<span class="hljs-params">list, observer</span>) =></span> { <span class="hljs-built_in">console</span>.log(list.getEntries()[<span class="hljs-number">0</span>]); performance.clearMarks(); observer.disconnect(); }); obs.observe({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'measure'</span>], <span class="hljs-attr">buffered</span>: <span class="hljs-literal">true</span> }); <span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> {}, <span class="hljs-number">1000</span>);</code></pre> <h3>Measuring how long it takes to load dependencies<span><a class="mark" href="#perf_hooks_measuring_how_long_it_takes_to_load_dependencies" id="perf_hooks_measuring_how_long_it_takes_to_load_dependencies">#</a></span></h3> <p>The following example measures the duration of <code>require()</code> operations to load dependencies:</p> <!-- eslint-disable no-global-assign --> <pre><code class="language-js"><span class="hljs-meta">'use strict'</span>; <span class="hljs-keyword">const</span> { performance, PerformanceObserver } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); <span class="hljs-keyword">const</span> mod = <span class="hljs-built_in">require</span>(<span class="hljs-string">'module'</span>); <span class="hljs-comment">// Monkey patch the require function</span> mod.Module.prototype.require = performance.timerify(mod.Module.prototype.require); <span class="hljs-built_in">require</span> = performance.timerify(<span class="hljs-built_in">require</span>); <span class="hljs-comment">// Activate the observer</span> <span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> PerformanceObserver(<span class="hljs-function">(<span class="hljs-params">list</span>) =></span> { <span class="hljs-keyword">const</span> entries = list.getEntries(); entries.forEach(<span class="hljs-function">(<span class="hljs-params">entry</span>) =></span> { <span class="hljs-built_in">console</span>.log(<span class="hljs-string">`require('<span class="hljs-subst">${entry[<span class="hljs-number">0</span>]}</span>')`</span>, entry.duration); }); obs.disconnect(); }); obs.observe({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'function'</span>], <span class="hljs-attr">buffered</span>: <span class="hljs-literal">true</span> }); <span class="hljs-built_in">require</span>(<span class="hljs-string">'some-module'</span>);</code></pre> <!-- API END --> </div> </div> </div> </body> </html>
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