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<div id="column1" data-id="perf_hooks" class="interior"> 90 <header> 91 <div class="header-container"> 92 <h1>Node.js v14.20.1 documentation</h1> 93 <button class="theme-toggle-btn" id="theme-toggle-btn" title="Toggle dark mode/light mode" aria-label="Toggle dark mode/light mode" hidden> 94 <svg xmlns="http://www.w3.org/2000/svg" class="icon dark-icon" height="24" width="24"> 95 <path fill="none" d="M0 0h24v24H0z" /> 96 <path d="M11.1 12.08c-2.33-4.51-.5-8.48.53-10.07C6.27 2.2 1.98 6.59 1.98 12c0 .14.02.28.02.42.62-.27 1.29-.42 2-.42 1.66 0 3.18.83 4.1 2.15A4.01 4.01 0 0111 18c0 1.52-.87 2.83-2.12 3.51.98.32 2.03.5 3.11.5 3.5 0 6.58-1.8 8.37-4.52-2.36.23-6.98-.97-9.26-5.41z"/> 97 <path d="M7 16h-.18C6.4 14.84 5.3 14 4 14c-1.66 0-3 1.34-3 3s1.34 3 3 3h3c1.1 0 2-.9 2-2s-.9-2-2-2z"/> 98 </svg> 99 <svg xmlns="http://www.w3.org/2000/svg" class="icon light-icon" height="24" width="24"> 100 <path d="M0 0h24v24H0z" fill="none" /> 101 <path d="M6.76 4.84l-1.8-1.79-1.41 1.41 1.79 1.79 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class="stability_2"><a href="#perf_hooks_performance_measurement_apis">Performance measurement APIs</a></span> 140<ul> 141<li><a href="#perf_hooks_perf_hooks_performance"><code>perf_hooks.performance</code></a> 142<ul> 143<li><a href="#perf_hooks_performance_clearmarks_name"><code>performance.clearMarks([name])</code></a></li> 144<li><a href="#perf_hooks_performance_eventlooputilization_utilization1_utilization2"><code>performance.eventLoopUtilization([utilization1[, utilization2]])</code></a></li> 145<li><a href="#perf_hooks_performance_mark_name"><code>performance.mark([name])</code></a></li> 146<li><a href="#perf_hooks_performance_measure_name_startmark_endmark"><code>performance.measure(name[, startMark[, endMark]])</code></a></li> 147<li><a href="#perf_hooks_performance_nodetiming"><code>performance.nodeTiming</code></a></li> 148<li><a href="#perf_hooks_performance_now"><code>performance.now()</code></a></li> 149<li><a href="#perf_hooks_performance_timeorigin"><code>performance.timeOrigin</code></a></li> 150<li><a href="#perf_hooks_performance_timerify_fn"><code>performance.timerify(fn)</code></a></li> 151</ul> 152</li> 153<li><a href="#perf_hooks_class_performanceentry">Class: <code>PerformanceEntry</code></a> 154<ul> 155<li><a href="#perf_hooks_performanceentry_duration"><code>performanceEntry.duration</code></a></li> 156<li><a href="#perf_hooks_performanceentry_entrytype"><code>performanceEntry.entryType</code></a></li> 157<li><a href="#perf_hooks_performanceentry_flags"><code>performanceEntry.flags</code></a></li> 158<li><a href="#perf_hooks_performanceentry_name"><code>performanceEntry.name</code></a></li> 159<li><a href="#perf_hooks_performanceentry_kind"><code>performanceEntry.kind</code></a></li> 160<li><a href="#perf_hooks_performanceentry_starttime"><code>performanceEntry.startTime</code></a></li> 161</ul> 162</li> 163<li><a href="#perf_hooks_class_performancenodetiming">Class: <code>PerformanceNodeTiming</code></a> 164<ul> 165<li><a href="#perf_hooks_performancenodetiming_bootstrapcomplete"><code>performanceNodeTiming.bootstrapComplete</code></a></li> 166<li><a href="#perf_hooks_performancenodetiming_environment"><code>performanceNodeTiming.environment</code></a></li> 167<li><a href="#perf_hooks_performancenodetiming_idletime"><code>performanceNodeTiming.idleTime</code></a></li> 168<li><a href="#perf_hooks_performancenodetiming_loopexit"><code>performanceNodeTiming.loopExit</code></a></li> 169<li><a href="#perf_hooks_performancenodetiming_loopstart"><code>performanceNodeTiming.loopStart</code></a></li> 170<li><a href="#perf_hooks_performancenodetiming_nodestart"><code>performanceNodeTiming.nodeStart</code></a></li> 171<li><a href="#perf_hooks_performancenodetiming_v8start"><code>performanceNodeTiming.v8Start</code></a></li> 172</ul> 173</li> 174<li><a href="#perf_hooks_class_perf_hooks_performanceobserver">Class: <code>perf_hooks.PerformanceObserver</code></a> 175<ul> 176<li><a href="#perf_hooks_new_performanceobserver_callback"><code>new PerformanceObserver(callback)</code></a></li> 177<li><a href="#perf_hooks_performanceobserver_disconnect"><code>performanceObserver.disconnect()</code></a></li> 178<li><a href="#perf_hooks_performanceobserver_observe_options"><code>performanceObserver.observe(options)</code></a></li> 179</ul> 180</li> 181<li><a href="#perf_hooks_class_performanceobserverentrylist">Class: <code>PerformanceObserverEntryList</code></a> 182<ul> 183<li><a href="#perf_hooks_performanceobserverentrylist_getentries"><code>performanceObserverEntryList.getEntries()</code></a></li> 184<li><a href="#perf_hooks_performanceobserverentrylist_getentriesbyname_name_type"><code>performanceObserverEntryList.getEntriesByName(name[, type])</code></a></li> 185<li><a href="#perf_hooks_performanceobserverentrylist_getentriesbytype_type"><code>performanceObserverEntryList.getEntriesByType(type)</code></a></li> 186</ul> 187</li> 188<li><a href="#perf_hooks_perf_hooks_createhistogram_options"><code>perf_hooks.createHistogram([options])</code></a></li> 189<li><a href="#perf_hooks_perf_hooks_monitoreventloopdelay_options"><code>perf_hooks.monitorEventLoopDelay([options])</code></a></li> 190<li><a href="#perf_hooks_class_histogram">Class: <code>Histogram</code></a> 191<ul> 192<li><a href="#perf_hooks_histogram_exceeds"><code>histogram.exceeds</code></a></li> 193<li><a href="#perf_hooks_histogram_max"><code>histogram.max</code></a></li> 194<li><a href="#perf_hooks_histogram_mean"><code>histogram.mean</code></a></li> 195<li><a href="#perf_hooks_histogram_min"><code>histogram.min</code></a></li> 196<li><a href="#perf_hooks_histogram_percentile_percentile"><code>histogram.percentile(percentile)</code></a></li> 197<li><a href="#perf_hooks_histogram_percentiles"><code>histogram.percentiles</code></a></li> 198<li><a href="#perf_hooks_histogram_reset"><code>histogram.reset()</code></a></li> 199<li><a href="#perf_hooks_histogram_stddev"><code>histogram.stddev</code></a></li> 200</ul> 201</li> 202<li><a href="#perf_hooks_class_intervalhistogram_extends_histogram">Class: <code>IntervalHistogram extends Histogram</code></a> 203<ul> 204<li><a href="#perf_hooks_histogram_disable"><code>histogram.disable()</code></a></li> 205<li><a href="#perf_hooks_histogram_enable"><code>histogram.enable()</code></a></li> 206<li><a href="#perf_hooks_cloning_an_intervalhistogram">Cloning an <code>IntervalHistogram</code></a></li> 207</ul> 208</li> 209<li><a href="#perf_hooks_class_recordablehistogram_extends_histogram">Class: <code>RecordableHistogram extends Histogram</code></a> 210<ul> 211<li><a href="#perf_hooks_histogram_record_val"><code>histogram.record(val)</code></a></li> 212<li><a href="#perf_hooks_histogram_recorddelta"><code>histogram.recordDelta()</code></a></li> 213</ul> 214</li> 215<li><a href="#perf_hooks_examples">Examples</a> 216<ul> 217<li><a href="#perf_hooks_measuring_the_duration_of_async_operations">Measuring the duration of async operations</a></li> 218<li><a href="#perf_hooks_measuring_how_long_it_takes_to_load_dependencies">Measuring how long it takes to load dependencies</a></li> 219</ul> 220</li> 221</ul> 222</li> 223</ul></details> 224 225 <div id="apicontent"> 226 <h2>Performance measurement APIs<span><a class="mark" href="#perf_hooks_performance_measurement_apis" id="perf_hooks_performance_measurement_apis">#</a></span></h2> 227 228<p></p><div class="api_stability api_stability_2"><a href="documentation.html#documentation_stability_index">Stability: 2</a> - Stable</div><p></p> 229<p><strong>Source Code:</strong> <a href="https://github.com/nodejs/node/blob/v14.20.1/lib/perf_hooks.js">lib/perf_hooks.js</a></p> 230<p>This module provides an implementation of a subset of the W3C 231<a href="https://w3c.github.io/perf-timing-primer/">Web Performance APIs</a> as well as additional APIs for 232Node.js-specific performance measurements.</p> 233<p>Node.js supports the following <a href="https://w3c.github.io/perf-timing-primer/">Web Performance APIs</a>:</p> 234<ul> 235<li><a href="https://www.w3.org/TR/hr-time-2">High Resolution Time</a></li> 236<li><a href="https://w3c.github.io/performance-timeline/">Performance Timeline</a></li> 237<li><a href="https://www.w3.org/TR/user-timing/">User Timing</a></li> 238</ul> 239<pre><code class="language-js"><span class="hljs-keyword">const</span> { <span class="hljs-title class_">PerformanceObserver</span>, performance } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); 240 241<span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> <span class="hljs-title class_">PerformanceObserver</span>(<span class="hljs-function">(<span class="hljs-params">items</span>) =></span> { 242 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(items.<span class="hljs-title function_">getEntries</span>()[<span class="hljs-number">0</span>].<span class="hljs-property">duration</span>); 243 performance.<span class="hljs-title function_">clearMarks</span>(); 244}); 245obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'measure'</span>] }); 246performance.<span class="hljs-title function_">measure</span>(<span class="hljs-string">'Start to Now'</span>); 247 248performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'A'</span>); 249<span class="hljs-title function_">doSomeLongRunningProcess</span>(<span class="hljs-function">() =></span> { 250 performance.<span class="hljs-title function_">measure</span>(<span class="hljs-string">'A to Now'</span>, <span class="hljs-string">'A'</span>); 251 252 performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'B'</span>); 253 performance.<span class="hljs-title function_">measure</span>(<span class="hljs-string">'A to B'</span>, <span class="hljs-string">'A'</span>, <span class="hljs-string">'B'</span>); 254});</code></pre> 255<section><h3><code>perf_hooks.performance</code><span><a class="mark" href="#perf_hooks_perf_hooks_performance" id="perf_hooks_perf_hooks_performance">#</a></span></h3> 256<div class="api_metadata"> 257<span>Added in: v8.5.0</span> 258</div> 259<p>An object that can be used to collect performance metrics from the current 260Node.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> 261<h4><code>performance.clearMarks([name])</code><span><a class="mark" href="#perf_hooks_performance_clearmarks_name" id="perf_hooks_performance_clearmarks_name">#</a></span></h4> 262<div class="api_metadata"> 263<span>Added in: v8.5.0</span> 264</div> 265<ul> 266<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 267</ul> 268<p>If <code>name</code> is not provided, removes all <code>PerformanceMark</code> objects from the 269Performance Timeline. If <code>name</code> is provided, removes only the named mark.</p> 270<h4><code>performance.eventLoopUtilization([utilization1[, utilization2]])</code><span><a class="mark" href="#perf_hooks_performance_eventlooputilization_utilization1_utilization2" id="perf_hooks_performance_eventlooputilization_utilization1_utilization2">#</a></span></h4> 271<div class="api_metadata"> 272<span>Added in: v14.10.0, v12.19.0</span> 273</div> 274<ul> 275<li><code>utilization1</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 276<code>eventLoopUtilization()</code>.</li> 277<li><code>utilization2</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 278<code>eventLoopUtilization()</code> prior to <code>utilization1</code>.</li> 279<li>Returns <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> 280<ul> 281<li><code>idle</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 282<li><code>active</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 283<li><code>utilization</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 284</ul> 285</li> 286</ul> 287<p>The <code>eventLoopUtilization()</code> method returns an object that contains the 288cumulative duration of time the event loop has been both idle and active as a 289high resolution milliseconds timer. The <code>utilization</code> value is the calculated 290Event Loop Utilization (ELU).</p> 291<p>If bootstrapping has not yet finished on the main thread the properties have 292the value of <code>0</code>. The ELU is immediately available on <a href="worker_threads.html#worker_threads_worker_threads">Worker threads</a> since 293bootstrap happens within the event loop.</p> 294<p>Both <code>utilization1</code> and <code>utilization2</code> are optional parameters.</p> 295<p>If <code>utilization1</code> is passed, then the delta between the current call's <code>active</code> 296and <code>idle</code> times, as well as the corresponding <code>utilization</code> value are 297calculated and returned (similar to <a href="process.html#process_process_hrtime_time"><code>process.hrtime()</code></a>).</p> 298<p>If <code>utilization1</code> and <code>utilization2</code> are both passed, then the delta is 299calculated between the two arguments. This is a convenience option because, 300unlike <a href="process.html#process_process_hrtime_time"><code>process.hrtime()</code></a>, calculating the ELU is more complex than a 301single subtraction.</p> 302<p>ELU is similar to CPU utilization, except that it only measures event loop 303statistics and not CPU usage. It represents the percentage of time the event 304loop has spent outside the event loop's event provider (e.g. <code>epoll_wait</code>). 305No other CPU idle time is taken into consideration. The following is an example 306of how a mostly idle process will have a high ELU.</p> 307<pre><code class="language-js"><span class="hljs-meta">'use strict'</span>; 308<span class="hljs-keyword">const</span> { eventLoopUtilization } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>).<span class="hljs-property">performance</span>; 309<span class="hljs-keyword">const</span> { spawnSync } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'child_process'</span>); 310 311<span class="hljs-title function_">setImmediate</span>(<span class="hljs-function">() =></span> { 312 <span class="hljs-keyword">const</span> elu = <span class="hljs-title function_">eventLoopUtilization</span>(); 313 <span class="hljs-title function_">spawnSync</span>(<span class="hljs-string">'sleep'</span>, [<span class="hljs-string">'5'</span>]); 314 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title function_">eventLoopUtilization</span>(elu).<span class="hljs-property">utilization</span>); 315});</code></pre> 316<p>Although the CPU is mostly idle while running this script, the value of 317<code>utilization</code> is <code>1</code>. This is because the call to 318<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> 319<p>Passing in a user-defined object instead of the result of a previous call to 320<code>eventLoopUtilization()</code> will lead to undefined behavior. The return values 321are not guaranteed to reflect any correct state of the event loop.</p> 322<h4><code>performance.mark([name])</code><span><a class="mark" href="#perf_hooks_performance_mark_name" id="perf_hooks_performance_mark_name">#</a></span></h4> 323<div class="api_metadata"> 324<span>Added in: v8.5.0</span> 325</div> 326<ul> 327<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 328</ul> 329<p>Creates a new <code>PerformanceMark</code> entry in the Performance Timeline. A 330<code>PerformanceMark</code> is a subclass of <code>PerformanceEntry</code> whose 331<code>performanceEntry.entryType</code> is always <code>'mark'</code>, and whose 332<code>performanceEntry.duration</code> is always <code>0</code>. Performance marks are used 333to mark specific significant moments in the Performance Timeline.</p> 334<h4><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></h4> 335<div class="api_metadata"> 336<details class="changelog"><summary>History</summary> 337<table> 338<tbody><tr><th>Version</th><th>Changes</th></tr> 339<tr><td>v14.0.0</td> 340<td><p>Make <code>startMark</code> and <code>endMark</code> parameters optional.</p></td></tr> 341<tr><td>v8.5.0</td> 342<td><p><span>Added in: v8.5.0</span></p></td></tr> 343</tbody></table> 344</details> 345</div> 346<ul> 347<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 348<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> 349<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> 350</ul> 351<p>Creates a new <code>PerformanceMeasure</code> entry in the Performance Timeline. A 352<code>PerformanceMeasure</code> is a subclass of <code>PerformanceEntry</code> whose 353<code>performanceEntry.entryType</code> is always <code>'measure'</code>, and whose 354<code>performanceEntry.duration</code> measures the number of milliseconds elapsed since 355<code>startMark</code> and <code>endMark</code>.</p> 356<p>The <code>startMark</code> argument may identify any <em>existing</em> <code>PerformanceMark</code> in the 357Performance Timeline, or <em>may</em> identify any of the timestamp properties 358provided by the <code>PerformanceNodeTiming</code> class. If the named <code>startMark</code> does 359not 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> 360<p>The optional <code>endMark</code> argument must identify any <em>existing</em> <code>PerformanceMark</code> 361in the Performance Timeline or any of the timestamp properties provided by the 362<code>PerformanceNodeTiming</code> class. <code>endMark</code> will be <code>performance.now()</code> 363if no parameter is passed, otherwise if the named <code>endMark</code> does not exist, an 364error will be thrown.</p> 365<h4><code>performance.nodeTiming</code><span><a class="mark" href="#perf_hooks_performance_nodetiming" id="perf_hooks_performance_nodetiming">#</a></span></h4> 366<div class="api_metadata"> 367<span>Added in: v8.5.0</span> 368</div> 369<ul> 370<li><a href="perf_hooks.html#perf_hooks_class_performancenodetiming" class="type"><PerformanceNodeTiming></a></li> 371</ul> 372<p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> 373<p>An instance of the <code>PerformanceNodeTiming</code> class that provides performance 374metrics for specific Node.js operational milestones.</p> 375<h4><code>performance.now()</code><span><a class="mark" href="#perf_hooks_performance_now" id="perf_hooks_performance_now">#</a></span></h4> 376<div class="api_metadata"> 377<span>Added in: v8.5.0</span> 378</div> 379<ul> 380<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 381</ul> 382<p>Returns the current high resolution millisecond timestamp, where 0 represents 383the start of the current <code>node</code> process.</p> 384<h4><code>performance.timeOrigin</code><span><a class="mark" href="#perf_hooks_performance_timeorigin" id="perf_hooks_performance_timeorigin">#</a></span></h4> 385<div class="api_metadata"> 386<span>Added in: v8.5.0</span> 387</div> 388<ul> 389<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 390</ul> 391<p>The <a href="https://w3c.github.io/hr-time/#dom-performance-timeorigin"><code>timeOrigin</code></a> specifies the high resolution millisecond timestamp at 392which the current <code>node</code> process began, measured in Unix time.</p> 393<h4><code>performance.timerify(fn)</code><span><a class="mark" href="#perf_hooks_performance_timerify_fn" id="perf_hooks_performance_timerify_fn">#</a></span></h4> 394<div class="api_metadata"> 395<span>Added in: v8.5.0</span> 396</div> 397<ul> 398<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li> 399</ul> 400<p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> 401<p>Wraps a function within a new function that measures the running time of the 402wrapped function. A <code>PerformanceObserver</code> must be subscribed to the <code>'function'</code> 403event type in order for the timing details to be accessed.</p> 404<pre><code class="language-js"><span class="hljs-keyword">const</span> { 405 performance, 406 <span class="hljs-title class_">PerformanceObserver</span> 407} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); 408 409<span class="hljs-keyword">function</span> <span class="hljs-title function_">someFunction</span>(<span class="hljs-params"></span>) { 410 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'hello world'</span>); 411} 412 413<span class="hljs-keyword">const</span> wrapped = performance.<span class="hljs-title function_">timerify</span>(someFunction); 414 415<span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> <span class="hljs-title class_">PerformanceObserver</span>(<span class="hljs-function">(<span class="hljs-params">list</span>) =></span> { 416 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(list.<span class="hljs-title function_">getEntries</span>()[<span class="hljs-number">0</span>].<span class="hljs-property">duration</span>); 417 obs.<span class="hljs-title function_">disconnect</span>(); 418}); 419obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'function'</span>] }); 420 421<span class="hljs-comment">// A performance timeline entry will be created</span> 422<span class="hljs-title function_">wrapped</span>();</code></pre> 423</section><section><h3>Class: <code>PerformanceEntry</code><span><a class="mark" href="#perf_hooks_class_performanceentry" id="perf_hooks_class_performanceentry">#</a></span></h3> 424<div class="api_metadata"> 425<span>Added in: v8.5.0</span> 426</div> 427<h4><code>performanceEntry.duration</code><span><a class="mark" href="#perf_hooks_performanceentry_duration" id="perf_hooks_performanceentry_duration">#</a></span></h4> 428<div class="api_metadata"> 429<span>Added in: v8.5.0</span> 430</div> 431<ul> 432<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 433</ul> 434<p>The total number of milliseconds elapsed for this entry. This value will not 435be meaningful for all Performance Entry types.</p> 436<h4><code>performanceEntry.entryType</code><span><a class="mark" href="#perf_hooks_performanceentry_entrytype" id="perf_hooks_performanceentry_entrytype">#</a></span></h4> 437<div class="api_metadata"> 438<span>Added in: v8.5.0</span> 439</div> 440<ul> 441<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 442</ul> 443<p>The type of the performance entry. It may be one of:</p> 444<ul> 445<li><code>'node'</code> (Node.js only)</li> 446<li><code>'mark'</code> (available on the Web)</li> 447<li><code>'measure'</code> (available on the Web)</li> 448<li><code>'gc'</code> (Node.js only)</li> 449<li><code>'function'</code> (Node.js only)</li> 450<li><code>'http2'</code> (Node.js only)</li> 451<li><code>'http'</code> (Node.js only)</li> 452</ul> 453<h4><code>performanceEntry.flags</code><span><a class="mark" href="#perf_hooks_performanceentry_flags" id="perf_hooks_performanceentry_flags">#</a></span></h4> 454<div class="api_metadata"> 455<span>Added in: v13.9.0, v12.17.0</span> 456</div> 457<ul> 458<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 459</ul> 460<p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> 461<p>When <code>performanceEntry.entryType</code> is equal to <code>'gc'</code>, the <code>performance.flags</code> 462property contains additional information about garbage collection operation. 463The value may be one of:</p> 464<ul> 465<li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_NO</code></li> 466<li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_CONSTRUCT_RETAINED</code></li> 467<li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_FORCED</code></li> 468<li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SYNCHRONOUS_PHANTOM_PROCESSING</code></li> 469<li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_AVAILABLE_GARBAGE</code></li> 470<li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_EXTERNAL_MEMORY</code></li> 471<li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SCHEDULE_IDLE</code></li> 472</ul> 473<h4><code>performanceEntry.name</code><span><a class="mark" href="#perf_hooks_performanceentry_name" id="perf_hooks_performanceentry_name">#</a></span></h4> 474<div class="api_metadata"> 475<span>Added in: v8.5.0</span> 476</div> 477<ul> 478<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 479</ul> 480<p>The name of the performance entry.</p> 481<h4><code>performanceEntry.kind</code><span><a class="mark" href="#perf_hooks_performanceentry_kind" id="perf_hooks_performanceentry_kind">#</a></span></h4> 482<div class="api_metadata"> 483<span>Added in: v8.5.0</span> 484</div> 485<ul> 486<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 487</ul> 488<p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> 489<p>When <code>performanceEntry.entryType</code> is equal to <code>'gc'</code>, the <code>performance.kind</code> 490property identifies the type of garbage collection operation that occurred. 491The value may be one of:</p> 492<ul> 493<li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_MAJOR</code></li> 494<li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_MINOR</code></li> 495<li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_INCREMENTAL</code></li> 496<li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_WEAKCB</code></li> 497</ul> 498<h4><code>performanceEntry.startTime</code><span><a class="mark" href="#perf_hooks_performanceentry_starttime" id="perf_hooks_performanceentry_starttime">#</a></span></h4> 499<div class="api_metadata"> 500<span>Added in: v8.5.0</span> 501</div> 502<ul> 503<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 504</ul> 505<p>The high resolution millisecond timestamp marking the starting time of the 506Performance Entry.</p> 507</section><section><h3>Class: <code>PerformanceNodeTiming</code><span><a class="mark" href="#perf_hooks_class_performancenodetiming" id="perf_hooks_class_performancenodetiming">#</a></span></h3> 508<div class="api_metadata"> 509<span>Added in: v8.5.0</span> 510</div> 511<ul> 512<li>Extends: <a href="perf_hooks.html#perf_hooks_class_performanceentry" class="type"><PerformanceEntry></a></li> 513</ul> 514<p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> 515<p>Provides timing details for Node.js itself. The constructor of this class 516is not exposed to users.</p> 517<h4><code>performanceNodeTiming.bootstrapComplete</code><span><a class="mark" href="#perf_hooks_performancenodetiming_bootstrapcomplete" id="perf_hooks_performancenodetiming_bootstrapcomplete">#</a></span></h4> 518<div class="api_metadata"> 519<span>Added in: v8.5.0</span> 520</div> 521<ul> 522<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 523</ul> 524<p>The high resolution millisecond timestamp at which the Node.js process 525completed bootstrapping. If bootstrapping has not yet finished, the property 526has the value of -1.</p> 527<h4><code>performanceNodeTiming.environment</code><span><a class="mark" href="#perf_hooks_performancenodetiming_environment" id="perf_hooks_performancenodetiming_environment">#</a></span></h4> 528<div class="api_metadata"> 529<span>Added in: v8.5.0</span> 530</div> 531<ul> 532<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 533</ul> 534<p>The high resolution millisecond timestamp at which the Node.js environment was 535initialized.</p> 536<h4><code>performanceNodeTiming.idleTime</code><span><a class="mark" href="#perf_hooks_performancenodetiming_idletime" id="perf_hooks_performancenodetiming_idletime">#</a></span></h4> 537<div class="api_metadata"> 538<span>Added in: v14.10.0, v12.19.0</span> 539</div> 540<ul> 541<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 542</ul> 543<p>The high resolution millisecond timestamp of the amount of time the event loop 544has been idle within the event loop's event provider (e.g. <code>epoll_wait</code>). This 545does not take CPU usage into consideration. If the event loop has not yet 546started (e.g., in the first tick of the main script), the property has the 547value of 0.</p> 548<h4><code>performanceNodeTiming.loopExit</code><span><a class="mark" href="#perf_hooks_performancenodetiming_loopexit" id="perf_hooks_performancenodetiming_loopexit">#</a></span></h4> 549<div class="api_metadata"> 550<span>Added in: v8.5.0</span> 551</div> 552<ul> 553<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 554</ul> 555<p>The high resolution millisecond timestamp at which the Node.js event loop 556exited. If the event loop has not yet exited, the property has the value of -1. 557It 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> 558<h4><code>performanceNodeTiming.loopStart</code><span><a class="mark" href="#perf_hooks_performancenodetiming_loopstart" id="perf_hooks_performancenodetiming_loopstart">#</a></span></h4> 559<div class="api_metadata"> 560<span>Added in: v8.5.0</span> 561</div> 562<ul> 563<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 564</ul> 565<p>The high resolution millisecond timestamp at which the Node.js event loop 566started. If the event loop has not yet started (e.g., in the first tick of the 567main script), the property has the value of -1.</p> 568<h4><code>performanceNodeTiming.nodeStart</code><span><a class="mark" href="#perf_hooks_performancenodetiming_nodestart" id="perf_hooks_performancenodetiming_nodestart">#</a></span></h4> 569<div class="api_metadata"> 570<span>Added in: v8.5.0</span> 571</div> 572<ul> 573<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 574</ul> 575<p>The high resolution millisecond timestamp at which the Node.js process was 576initialized.</p> 577<h4><code>performanceNodeTiming.v8Start</code><span><a class="mark" href="#perf_hooks_performancenodetiming_v8start" id="perf_hooks_performancenodetiming_v8start">#</a></span></h4> 578<div class="api_metadata"> 579<span>Added in: v8.5.0</span> 580</div> 581<ul> 582<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 583</ul> 584<p>The high resolution millisecond timestamp at which the V8 platform was 585initialized.</p> 586</section><section><h3>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></h3> 587<h4><code>new PerformanceObserver(callback)</code><span><a class="mark" href="#perf_hooks_new_performanceobserver_callback" id="perf_hooks_new_performanceobserver_callback">#</a></span></h4> 588<div class="api_metadata"> 589<span>Added in: v8.5.0</span> 590</div> 591<ul> 592<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> 593<ul> 594<li><code>list</code> <a href="perf_hooks.html#perf_hooks_class_performanceobserverentrylist" class="type"><PerformanceObserverEntryList></a></li> 595<li><code>observer</code> <a href="perf_hooks.html#perf_hooks_class_perf_hooks_performanceobserver" class="type"><PerformanceObserver></a></li> 596</ul> 597</li> 598</ul> 599<p><code>PerformanceObserver</code> objects provide notifications when new 600<code>PerformanceEntry</code> instances have been added to the Performance Timeline.</p> 601<pre><code class="language-js"><span class="hljs-keyword">const</span> { 602 performance, 603 <span class="hljs-title class_">PerformanceObserver</span> 604} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); 605 606<span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> <span class="hljs-title class_">PerformanceObserver</span>(<span class="hljs-function">(<span class="hljs-params">list, observer</span>) =></span> { 607 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(list.<span class="hljs-title function_">getEntries</span>()); 608 observer.<span class="hljs-title function_">disconnect</span>(); 609}); 610obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'mark'</span>], <span class="hljs-attr">buffered</span>: <span class="hljs-literal">true</span> }); 611 612performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'test'</span>);</code></pre> 613<p>Because <code>PerformanceObserver</code> instances introduce their own additional 614performance overhead, instances should not be left subscribed to notifications 615indefinitely. Users should disconnect observers as soon as they are no 616longer needed.</p> 617<p>The <code>callback</code> is invoked when a <code>PerformanceObserver</code> is 618notified about new <code>PerformanceEntry</code> instances. The callback receives a 619<code>PerformanceObserverEntryList</code> instance and a reference to the 620<code>PerformanceObserver</code>.</p> 621<h4><code>performanceObserver.disconnect()</code><span><a class="mark" href="#perf_hooks_performanceobserver_disconnect" id="perf_hooks_performanceobserver_disconnect">#</a></span></h4> 622<div class="api_metadata"> 623<span>Added in: v8.5.0</span> 624</div> 625<p>Disconnects the <code>PerformanceObserver</code> instance from all notifications.</p> 626<h4><code>performanceObserver.observe(options)</code><span><a class="mark" href="#perf_hooks_performanceobserver_observe_options" id="perf_hooks_performanceobserver_observe_options">#</a></span></h4> 627<div class="api_metadata"> 628<span>Added in: v8.5.0</span> 629</div> 630<ul> 631<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> 632<ul> 633<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 634<code>PerformanceEntry</code> instances the observer is interested in. If not 635provided an error will be thrown.</li> 636<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 637called using <code>setImmediate()</code> and multiple <code>PerformanceEntry</code> instance 638notifications will be buffered internally. If <code>false</code>, notifications will 639be immediate and synchronous. <strong>Default:</strong> <code>false</code>.</li> 640</ul> 641</li> 642</ul> 643<p>Subscribes the <code>PerformanceObserver</code> instance to notifications of new 644<code>PerformanceEntry</code> instances identified by <code>options.entryTypes</code>.</p> 645<p>When <code>options.buffered</code> is <code>false</code>, the <code>callback</code> will be invoked once for 646every <code>PerformanceEntry</code> instance:</p> 647<pre><code class="language-js"><span class="hljs-keyword">const</span> { 648 performance, 649 <span class="hljs-title class_">PerformanceObserver</span> 650} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); 651 652<span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> <span class="hljs-title class_">PerformanceObserver</span>(<span class="hljs-function">(<span class="hljs-params">list, observer</span>) =></span> { 653 <span class="hljs-comment">// Called three times synchronously. `list` contains one item.</span> 654}); 655obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'mark'</span>] }); 656 657<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++) 658 performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">`test<span class="hljs-subst">${n}</span>`</span>);</code></pre> 659<pre><code class="language-js"><span class="hljs-keyword">const</span> { 660 performance, 661 <span class="hljs-title class_">PerformanceObserver</span> 662} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); 663 664<span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> <span class="hljs-title class_">PerformanceObserver</span>(<span class="hljs-function">(<span class="hljs-params">list, observer</span>) =></span> { 665 <span class="hljs-comment">// Called once. `list` contains three items.</span> 666}); 667obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'mark'</span>], <span class="hljs-attr">buffered</span>: <span class="hljs-literal">true</span> }); 668 669<span class="hljs-keyword">for</span> (<span class="hljs-keyword">let</span> n = <span class="hljs-number">0</span>; n < <span class="hljs-number">3</span>; n++) 670 performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">`test<span class="hljs-subst">${n}</span>`</span>);</code></pre> 671</section><section><h3>Class: <code>PerformanceObserverEntryList</code><span><a class="mark" href="#perf_hooks_class_performanceobserverentrylist" id="perf_hooks_class_performanceobserverentrylist">#</a></span></h3> 672<div class="api_metadata"> 673<span>Added in: v8.5.0</span> 674</div> 675<p>The <code>PerformanceObserverEntryList</code> class is used to provide access to the 676<code>PerformanceEntry</code> instances passed to a <code>PerformanceObserver</code>. 677The constructor of this class is not exposed to users.</p> 678<h4><code>performanceObserverEntryList.getEntries()</code><span><a class="mark" href="#perf_hooks_performanceobserverentrylist_getentries" id="perf_hooks_performanceobserverentrylist_getentries">#</a></span></h4> 679<div class="api_metadata"> 680<span>Added in: v8.5.0</span> 681</div> 682<ul> 683<li>Returns: <a href="perf_hooks.html#perf_hooks_class_performanceentry" class="type"><PerformanceEntry[]></a></li> 684</ul> 685<p>Returns a list of <code>PerformanceEntry</code> objects in chronological order 686with respect to <code>performanceEntry.startTime</code>.</p> 687<pre><code class="language-js"><span class="hljs-keyword">const</span> { 688 performance, 689 <span class="hljs-title class_">PerformanceObserver</span> 690} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); 691 692<span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> <span class="hljs-title class_">PerformanceObserver</span>(<span class="hljs-function">(<span class="hljs-params">perfObserverList, observer</span>) =></span> { 693 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(perfObserverList.<span class="hljs-title function_">getEntries</span>()); 694 <span class="hljs-comment">/** 695 * [ 696 * PerformanceEntry { 697 * name: 'test', 698 * entryType: 'mark', 699 * startTime: 81.465639, 700 * duration: 0 701 * }, 702 * PerformanceEntry { 703 * name: 'meow', 704 * entryType: 'mark', 705 * startTime: 81.860064, 706 * duration: 0 707 * } 708 * ] 709 */</span> 710 observer.<span class="hljs-title function_">disconnect</span>(); 711}); 712obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'mark'</span>], <span class="hljs-attr">buffered</span>: <span class="hljs-literal">true</span> }); 713 714performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'test'</span>); 715performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'meow'</span>);</code></pre> 716<h4><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></h4> 717<div class="api_metadata"> 718<span>Added in: v8.5.0</span> 719</div> 720<ul> 721<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 722<li><code>type</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 723<li>Returns: <a href="perf_hooks.html#perf_hooks_class_performanceentry" class="type"><PerformanceEntry[]></a></li> 724</ul> 725<p>Returns a list of <code>PerformanceEntry</code> objects in chronological order 726with respect to <code>performanceEntry.startTime</code> whose <code>performanceEntry.name</code> is 727equal to <code>name</code>, and optionally, whose <code>performanceEntry.entryType</code> is equal to 728<code>type</code>.</p> 729<pre><code class="language-js"><span class="hljs-keyword">const</span> { 730 performance, 731 <span class="hljs-title class_">PerformanceObserver</span> 732} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); 733 734<span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> <span class="hljs-title class_">PerformanceObserver</span>(<span class="hljs-function">(<span class="hljs-params">perfObserverList, observer</span>) =></span> { 735 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(perfObserverList.<span class="hljs-title function_">getEntriesByName</span>(<span class="hljs-string">'meow'</span>)); 736 <span class="hljs-comment">/** 737 * [ 738 * PerformanceEntry { 739 * name: 'meow', 740 * entryType: 'mark', 741 * startTime: 98.545991, 742 * duration: 0 743 * } 744 * ] 745 */</span> 746 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(perfObserverList.<span class="hljs-title function_">getEntriesByName</span>(<span class="hljs-string">'nope'</span>)); <span class="hljs-comment">// []</span> 747 748 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(perfObserverList.<span class="hljs-title function_">getEntriesByName</span>(<span class="hljs-string">'test'</span>, <span class="hljs-string">'mark'</span>)); 749 <span class="hljs-comment">/** 750 * [ 751 * PerformanceEntry { 752 * name: 'test', 753 * entryType: 'mark', 754 * startTime: 63.518931, 755 * duration: 0 756 * } 757 * ] 758 */</span> 759 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(perfObserverList.<span class="hljs-title function_">getEntriesByName</span>(<span class="hljs-string">'test'</span>, <span class="hljs-string">'measure'</span>)); <span class="hljs-comment">// []</span> 760 observer.<span class="hljs-title function_">disconnect</span>(); 761}); 762obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'mark'</span>, <span class="hljs-string">'measure'</span>], <span class="hljs-attr">buffered</span>: <span class="hljs-literal">true</span> }); 763 764performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'test'</span>); 765performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'meow'</span>);</code></pre> 766<h4><code>performanceObserverEntryList.getEntriesByType(type)</code><span><a class="mark" href="#perf_hooks_performanceobserverentrylist_getentriesbytype_type" id="perf_hooks_performanceobserverentrylist_getentriesbytype_type">#</a></span></h4> 767<div class="api_metadata"> 768<span>Added in: v8.5.0</span> 769</div> 770<ul> 771<li><code>type</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 772<li>Returns: <a href="perf_hooks.html#perf_hooks_class_performanceentry" class="type"><PerformanceEntry[]></a></li> 773</ul> 774<p>Returns a list of <code>PerformanceEntry</code> objects in chronological order 775with respect to <code>performanceEntry.startTime</code> whose <code>performanceEntry.entryType</code> 776is equal to <code>type</code>.</p> 777<pre><code class="language-js"><span class="hljs-keyword">const</span> { 778 performance, 779 <span class="hljs-title class_">PerformanceObserver</span> 780} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); 781 782<span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> <span class="hljs-title class_">PerformanceObserver</span>(<span class="hljs-function">(<span class="hljs-params">perfObserverList, observer</span>) =></span> { 783 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(perfObserverList.<span class="hljs-title function_">getEntriesByType</span>(<span class="hljs-string">'mark'</span>)); 784 <span class="hljs-comment">/** 785 * [ 786 * PerformanceEntry { 787 * name: 'test', 788 * entryType: 'mark', 789 * startTime: 55.897834, 790 * duration: 0 791 * }, 792 * PerformanceEntry { 793 * name: 'meow', 794 * entryType: 'mark', 795 * startTime: 56.350146, 796 * duration: 0 797 * } 798 * ] 799 */</span> 800 observer.<span class="hljs-title function_">disconnect</span>(); 801}); 802obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'mark'</span>], <span class="hljs-attr">buffered</span>: <span class="hljs-literal">true</span> }); 803 804performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'test'</span>); 805performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'meow'</span>);</code></pre> 806</section><section><h3><code>perf_hooks.createHistogram([options])</code><span><a class="mark" href="#perf_hooks_perf_hooks_createhistogram_options" id="perf_hooks_perf_hooks_createhistogram_options">#</a></span></h3> 807<div class="api_metadata"> 808<span>Added in: v14.18.0</span> 809</div> 810<ul> 811<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> 812<ul> 813<li><code>min</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt" class="type"><bigint></a> The minimum recordable value. Must be an integer 814value greater than 0. <strong>Defaults</strong>: <code>1</code>.</li> 815<li><code>max</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt" class="type"><bigint></a> The maximum recordable value. Must be an integer 816value greater than <code>min</code>. <strong>Defaults</strong>: <code>Number.MAX_SAFE_INTEGER</code>.</li> 817<li><code>figures</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The number of accuracy digits. Must be a number between 818<code>1</code> and <code>5</code>. <strong>Defaults</strong>: <code>3</code>.</li> 819</ul> 820</li> 821<li>Returns <a href="perf_hooks.html#perf_hooks_class_recordablehistogram_extends_histogram" class="type"><RecordableHistogram></a></li> 822</ul> 823<p>Returns a <a href="perf_hooks.html#perf_hooks_class_recordablehistogram_extends_histogram" class="type"><RecordableHistogram></a>.</p> 824</section><section><h3><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></h3> 825<div class="api_metadata"> 826<span>Added in: v11.10.0</span> 827</div> 828<ul> 829<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> 830<ul> 831<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 832than zero. <strong>Default:</strong> <code>10</code>.</li> 833</ul> 834</li> 835<li>Returns: <a href="perf_hooks.html#perf_hooks_class_intervalhistogram_extends_histogram" class="type"><IntervalHistogram></a></li> 836</ul> 837<p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> 838<p>Creates an <code>IntervalHistogram</code> object that samples and reports the event loop 839delay over time. The delays will be reported in nanoseconds.</p> 840<p>Using a timer to detect approximate event loop delay works because the 841execution of timers is tied specifically to the lifecycle of the libuv 842event loop. That is, a delay in the loop will cause a delay in the execution 843of the timer, and those delays are specifically what this API is intended to 844detect.</p> 845<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>); 846<span class="hljs-keyword">const</span> h = <span class="hljs-title function_">monitorEventLoopDelay</span>({ <span class="hljs-attr">resolution</span>: <span class="hljs-number">20</span> }); 847h.<span class="hljs-title function_">enable</span>(); 848<span class="hljs-comment">// Do something.</span> 849h.<span class="hljs-title function_">disable</span>(); 850<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(h.<span class="hljs-property">min</span>); 851<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(h.<span class="hljs-property">max</span>); 852<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(h.<span class="hljs-property">mean</span>); 853<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(h.<span class="hljs-property">stddev</span>); 854<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(h.<span class="hljs-property">percentiles</span>); 855<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(h.<span class="hljs-title function_">percentile</span>(<span class="hljs-number">50</span>)); 856<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(h.<span class="hljs-title function_">percentile</span>(<span class="hljs-number">99</span>));</code></pre> 857</section><section><h3>Class: <code>Histogram</code><span><a class="mark" href="#perf_hooks_class_histogram" id="perf_hooks_class_histogram">#</a></span></h3> 858<div class="api_metadata"> 859<span>Added in: v11.10.0</span> 860</div> 861<h4><code>histogram.exceeds</code><span><a class="mark" href="#perf_hooks_histogram_exceeds" id="perf_hooks_histogram_exceeds">#</a></span></h4> 862<div class="api_metadata"> 863<span>Added in: v11.10.0</span> 864</div> 865<ul> 866<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 867</ul> 868<p>The number of times the event loop delay exceeded the maximum 1 hour event 869loop delay threshold.</p> 870<h4><code>histogram.max</code><span><a class="mark" href="#perf_hooks_histogram_max" id="perf_hooks_histogram_max">#</a></span></h4> 871<div class="api_metadata"> 872<span>Added in: v11.10.0</span> 873</div> 874<ul> 875<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 876</ul> 877<p>The maximum recorded event loop delay.</p> 878<h4><code>histogram.mean</code><span><a class="mark" href="#perf_hooks_histogram_mean" id="perf_hooks_histogram_mean">#</a></span></h4> 879<div class="api_metadata"> 880<span>Added in: v11.10.0</span> 881</div> 882<ul> 883<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 884</ul> 885<p>The mean of the recorded event loop delays.</p> 886<h4><code>histogram.min</code><span><a class="mark" href="#perf_hooks_histogram_min" id="perf_hooks_histogram_min">#</a></span></h4> 887<div class="api_metadata"> 888<span>Added in: v11.10.0</span> 889</div> 890<ul> 891<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 892</ul> 893<p>The minimum recorded event loop delay.</p> 894<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> 895<div class="api_metadata"> 896<span>Added in: v11.10.0</span> 897</div> 898<ul> 899<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 in the range (0, 100].</li> 900<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 901</ul> 902<p>Returns the value at the given percentile.</p> 903<h4><code>histogram.percentiles</code><span><a class="mark" href="#perf_hooks_histogram_percentiles" id="perf_hooks_histogram_percentiles">#</a></span></h4> 904<div class="api_metadata"> 905<span>Added in: v11.10.0</span> 906</div> 907<ul> 908<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map" class="type"><Map></a></li> 909</ul> 910<p>Returns a <code>Map</code> object detailing the accumulated percentile distribution.</p> 911<h4><code>histogram.reset()</code><span><a class="mark" href="#perf_hooks_histogram_reset" id="perf_hooks_histogram_reset">#</a></span></h4> 912<div class="api_metadata"> 913<span>Added in: v11.10.0</span> 914</div> 915<p>Resets the collected histogram data.</p> 916<h4><code>histogram.stddev</code><span><a class="mark" href="#perf_hooks_histogram_stddev" id="perf_hooks_histogram_stddev">#</a></span></h4> 917<div class="api_metadata"> 918<span>Added in: v11.10.0</span> 919</div> 920<ul> 921<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 922</ul> 923<p>The standard deviation of the recorded event loop delays.</p> 924</section><section><h3>Class: <code>IntervalHistogram extends Histogram</code><span><a class="mark" href="#perf_hooks_class_intervalhistogram_extends_histogram" id="perf_hooks_class_intervalhistogram_extends_histogram">#</a></span></h3> 925<p>A <code>Histogram</code> that is periodically updated on a given interval.</p> 926<h4><code>histogram.disable()</code><span><a class="mark" href="#perf_hooks_histogram_disable" id="perf_hooks_histogram_disable">#</a></span></h4> 927<div class="api_metadata"> 928<span>Added in: v11.10.0</span> 929</div> 930<ul> 931<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> 932</ul> 933<p>Disables the update interval timer. Returns <code>true</code> if the timer was 934stopped, <code>false</code> if it was already stopped.</p> 935<h4><code>histogram.enable()</code><span><a class="mark" href="#perf_hooks_histogram_enable" id="perf_hooks_histogram_enable">#</a></span></h4> 936<div class="api_metadata"> 937<span>Added in: v11.10.0</span> 938</div> 939<ul> 940<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> 941</ul> 942<p>Enables the update interval timer. Returns <code>true</code> if the timer was 943started, <code>false</code> if it was already started.</p> 944<h4>Cloning an <code>IntervalHistogram</code><span><a class="mark" href="#perf_hooks_cloning_an_intervalhistogram" id="perf_hooks_cloning_an_intervalhistogram">#</a></span></h4> 945<p><a href="perf_hooks.html#perf_hooks_class_intervalhistogram_extends_histogram" class="type"><IntervalHistogram></a> instances can be cloned via <a href="worker_threads.html#worker_threads_class_messageport" class="type"><MessagePort></a>. On the receiving 946end, the histogram is cloned as a plain <a href="perf_hooks.html#perf_hooks_class_histogram" class="type"><Histogram></a> object that does not 947implement the <code>enable()</code> and <code>disable()</code> methods.</p> 948</section><section><h3>Class: <code>RecordableHistogram extends Histogram</code><span><a class="mark" href="#perf_hooks_class_recordablehistogram_extends_histogram" id="perf_hooks_class_recordablehistogram_extends_histogram">#</a></span></h3> 949<div class="api_metadata"> 950<span>Added in: v14.18.0</span> 951</div> 952<h4><code>histogram.record(val)</code><span><a class="mark" href="#perf_hooks_histogram_record_val" id="perf_hooks_histogram_record_val">#</a></span></h4> 953<div class="api_metadata"> 954<span>Added in: v14.18.0</span> 955</div> 956<ul> 957<li><code>val</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt" class="type"><bigint></a> The amount to record in the histogram.</li> 958</ul> 959<h4><code>histogram.recordDelta()</code><span><a class="mark" href="#perf_hooks_histogram_recorddelta" id="perf_hooks_histogram_recorddelta">#</a></span></h4> 960<div class="api_metadata"> 961<span>Added in: v14.18.0</span> 962</div> 963<p>Calculates the amount of time (in nanoseconds) that has passed since the 964previous call to <code>recordDelta()</code> and records that amount in the histogram.</p> 965</section><section><h3>Examples<span><a class="mark" href="#perf_hooks_examples" id="perf_hooks_examples">#</a></span></h3> 966<h4>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></h4> 967<p>The following example uses the <a href="async_hooks.html">Async Hooks</a> and Performance APIs to measure 968the actual duration of a Timeout operation (including the amount of time it took 969to execute the callback).</p> 970<pre><code class="language-js"><span class="hljs-meta">'use strict'</span>; 971<span class="hljs-keyword">const</span> async_hooks = <span class="hljs-built_in">require</span>(<span class="hljs-string">'async_hooks'</span>); 972<span class="hljs-keyword">const</span> { 973 performance, 974 <span class="hljs-title class_">PerformanceObserver</span> 975} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); 976 977<span class="hljs-keyword">const</span> set = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Set</span>(); 978<span class="hljs-keyword">const</span> hook = async_hooks.<span class="hljs-title function_">createHook</span>({ 979 <span class="hljs-title function_">init</span>(<span class="hljs-params">id, type</span>) { 980 <span class="hljs-keyword">if</span> (type === <span class="hljs-string">'Timeout'</span>) { 981 performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">`Timeout-<span class="hljs-subst">${id}</span>-Init`</span>); 982 set.<span class="hljs-title function_">add</span>(id); 983 } 984 }, 985 <span class="hljs-title function_">destroy</span>(<span class="hljs-params">id</span>) { 986 <span class="hljs-keyword">if</span> (set.<span class="hljs-title function_">has</span>(id)) { 987 set.<span class="hljs-title function_">delete</span>(id); 988 performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">`Timeout-<span class="hljs-subst">${id}</span>-Destroy`</span>); 989 performance.<span class="hljs-title function_">measure</span>(<span class="hljs-string">`Timeout-<span class="hljs-subst">${id}</span>`</span>, 990 <span class="hljs-string">`Timeout-<span class="hljs-subst">${id}</span>-Init`</span>, 991 <span class="hljs-string">`Timeout-<span class="hljs-subst">${id}</span>-Destroy`</span>); 992 } 993 } 994}); 995hook.<span class="hljs-title function_">enable</span>(); 996 997<span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> <span class="hljs-title class_">PerformanceObserver</span>(<span class="hljs-function">(<span class="hljs-params">list, observer</span>) =></span> { 998 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(list.<span class="hljs-title function_">getEntries</span>()[<span class="hljs-number">0</span>]); 999 performance.<span class="hljs-title function_">clearMarks</span>(); 1000 observer.<span class="hljs-title function_">disconnect</span>(); 1001}); 1002obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'measure'</span>], <span class="hljs-attr">buffered</span>: <span class="hljs-literal">true</span> }); 1003 1004<span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> {}, <span class="hljs-number">1000</span>);</code></pre> 1005<h4>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></h4> 1006<p>The following example measures the duration of <code>require()</code> operations to load 1007dependencies:</p> 1008<!-- eslint-disable no-global-assign --> 1009<pre><code class="language-js"><span class="hljs-meta">'use strict'</span>; 1010<span class="hljs-keyword">const</span> { 1011 performance, 1012 <span class="hljs-title class_">PerformanceObserver</span> 1013} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); 1014<span class="hljs-keyword">const</span> mod = <span class="hljs-built_in">require</span>(<span class="hljs-string">'module'</span>); 1015 1016<span class="hljs-comment">// Monkey patch the require function</span> 1017mod.<span class="hljs-property">Module</span>.<span class="hljs-property"><span class="hljs-keyword">prototype</span></span>.<span class="hljs-property">require</span> = 1018 performance.<span class="hljs-title function_">timerify</span>(mod.<span class="hljs-property">Module</span>.<span class="hljs-property"><span class="hljs-keyword">prototype</span></span>.<span class="hljs-property">require</span>); 1019<span class="hljs-built_in">require</span> = performance.<span class="hljs-title function_">timerify</span>(<span class="hljs-built_in">require</span>); 1020 1021<span class="hljs-comment">// Activate the observer</span> 1022<span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> <span class="hljs-title class_">PerformanceObserver</span>(<span class="hljs-function">(<span class="hljs-params">list</span>) =></span> { 1023 <span class="hljs-keyword">const</span> entries = list.<span class="hljs-title function_">getEntries</span>(); 1024 entries.<span class="hljs-title function_">forEach</span>(<span class="hljs-function">(<span class="hljs-params">entry</span>) =></span> { 1025 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`require('<span class="hljs-subst">${entry[<span class="hljs-number">0</span>]}</span>')`</span>, entry.<span class="hljs-property">duration</span>); 1026 }); 1027 obs.<span class="hljs-title function_">disconnect</span>(); 1028}); 1029obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'function'</span>], <span class="hljs-attr">buffered</span>: <span class="hljs-literal">true</span> }); 1030 1031<span class="hljs-built_in">require</span>(<span class="hljs-string">'some-module'</span>);</code></pre></section> 1032 <!-- API END --> 1033 </div> 1034 </div> 1035 </div> 1036 <script> 1037 'use strict'; 1038 { 1039 const kCustomPreference = 'customDarkTheme'; 1040 const userSettings = sessionStorage.getItem(kCustomPreference); 1041 const themeToggleButton = document.getElementById('theme-toggle-btn'); 1042 if (userSettings === null && window.matchMedia) { 1043 const mq = window.matchMedia('(prefers-color-scheme: dark)'); 1044 if ('onchange' in mq) { 1045 function mqChangeListener(e) { 1046 document.body.classList.toggle('dark-mode', e.matches); 1047 } 1048 mq.addEventListener('change', mqChangeListener); 1049 if (themeToggleButton) { 1050 themeToggleButton.addEventListener('click', function() { 1051 mq.removeEventListener('change', mqChangeListener); 1052 }, { once: true }); 1053 } 1054 } 1055 if (mq.matches) { 1056 document.body.classList.add('dark-mode'); 1057 } 1058 } else if (userSettings === 'true') { 1059 document.body.classList.add('dark-mode'); 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