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<div id="column1" data-id="perf_hooks" class="interior"> 90 <header> 91 <div class="header-container"> 92 <h1>Node.js v14.19.1 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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APIs</a></span> 139<ul> 140<li><a href="#perf_hooks_perf_hooks_performance"><code>perf_hooks.performance</code></a> 141<ul> 142<li><a href="#perf_hooks_performance_clearmarks_name"><code>performance.clearMarks([name])</code></a></li> 143<li><a href="#perf_hooks_performance_eventlooputilization_utilization1_utilization2"><code>performance.eventLoopUtilization([utilization1[, utilization2]])</code></a></li> 144<li><a href="#perf_hooks_performance_mark_name"><code>performance.mark([name])</code></a></li> 145<li><a href="#perf_hooks_performance_measure_name_startmark_endmark"><code>performance.measure(name[, startMark[, endMark]])</code></a></li> 146<li><a href="#perf_hooks_performance_nodetiming"><code>performance.nodeTiming</code></a></li> 147<li><a href="#perf_hooks_performance_now"><code>performance.now()</code></a></li> 148<li><a href="#perf_hooks_performance_timeorigin"><code>performance.timeOrigin</code></a></li> 149<li><a href="#perf_hooks_performance_timerify_fn"><code>performance.timerify(fn)</code></a></li> 150</ul> 151</li> 152<li><a href="#perf_hooks_class_performanceentry">Class: <code>PerformanceEntry</code></a> 153<ul> 154<li><a href="#perf_hooks_performanceentry_duration"><code>performanceEntry.duration</code></a></li> 155<li><a href="#perf_hooks_performanceentry_entrytype"><code>performanceEntry.entryType</code></a></li> 156<li><a href="#perf_hooks_performanceentry_flags"><code>performanceEntry.flags</code></a></li> 157<li><a href="#perf_hooks_performanceentry_name"><code>performanceEntry.name</code></a></li> 158<li><a href="#perf_hooks_performanceentry_kind"><code>performanceEntry.kind</code></a></li> 159<li><a href="#perf_hooks_performanceentry_starttime"><code>performanceEntry.startTime</code></a></li> 160</ul> 161</li> 162<li><a href="#perf_hooks_class_performancenodetiming">Class: <code>PerformanceNodeTiming</code></a> 163<ul> 164<li><a href="#perf_hooks_performancenodetiming_bootstrapcomplete"><code>performanceNodeTiming.bootstrapComplete</code></a></li> 165<li><a href="#perf_hooks_performancenodetiming_environment"><code>performanceNodeTiming.environment</code></a></li> 166<li><a href="#perf_hooks_performancenodetiming_idletime"><code>performanceNodeTiming.idleTime</code></a></li> 167<li><a href="#perf_hooks_performancenodetiming_loopexit"><code>performanceNodeTiming.loopExit</code></a></li> 168<li><a href="#perf_hooks_performancenodetiming_loopstart"><code>performanceNodeTiming.loopStart</code></a></li> 169<li><a href="#perf_hooks_performancenodetiming_nodestart"><code>performanceNodeTiming.nodeStart</code></a></li> 170<li><a href="#perf_hooks_performancenodetiming_v8start"><code>performanceNodeTiming.v8Start</code></a></li> 171</ul> 172</li> 173<li><a href="#perf_hooks_class_perf_hooks_performanceobserver">Class: <code>perf_hooks.PerformanceObserver</code></a> 174<ul> 175<li><a href="#perf_hooks_new_performanceobserver_callback"><code>new PerformanceObserver(callback)</code></a></li> 176<li><a href="#perf_hooks_performanceobserver_disconnect"><code>performanceObserver.disconnect()</code></a></li> 177<li><a href="#perf_hooks_performanceobserver_observe_options"><code>performanceObserver.observe(options)</code></a></li> 178</ul> 179</li> 180<li><a href="#perf_hooks_class_performanceobserverentrylist">Class: <code>PerformanceObserverEntryList</code></a> 181<ul> 182<li><a href="#perf_hooks_performanceobserverentrylist_getentries"><code>performanceObserverEntryList.getEntries()</code></a></li> 183<li><a href="#perf_hooks_performanceobserverentrylist_getentriesbyname_name_type"><code>performanceObserverEntryList.getEntriesByName(name[, type])</code></a></li> 184<li><a href="#perf_hooks_performanceobserverentrylist_getentriesbytype_type"><code>performanceObserverEntryList.getEntriesByType(type)</code></a></li> 185</ul> 186</li> 187<li><a href="#perf_hooks_perf_hooks_createhistogram_options"><code>perf_hooks.createHistogram([options])</code></a></li> 188<li><a href="#perf_hooks_perf_hooks_monitoreventloopdelay_options"><code>perf_hooks.monitorEventLoopDelay([options])</code></a></li> 189<li><a href="#perf_hooks_class_histogram">Class: <code>Histogram</code></a> 190<ul> 191<li><a href="#perf_hooks_histogram_exceeds"><code>histogram.exceeds</code></a></li> 192<li><a href="#perf_hooks_histogram_max"><code>histogram.max</code></a></li> 193<li><a href="#perf_hooks_histogram_mean"><code>histogram.mean</code></a></li> 194<li><a href="#perf_hooks_histogram_min"><code>histogram.min</code></a></li> 195<li><a href="#perf_hooks_histogram_percentile_percentile"><code>histogram.percentile(percentile)</code></a></li> 196<li><a href="#perf_hooks_histogram_percentiles"><code>histogram.percentiles</code></a></li> 197<li><a href="#perf_hooks_histogram_reset"><code>histogram.reset()</code></a></li> 198<li><a href="#perf_hooks_histogram_stddev"><code>histogram.stddev</code></a></li> 199</ul> 200</li> 201<li><a href="#perf_hooks_class_intervalhistogram_extends_histogram">Class: <code>IntervalHistogram extends Histogram</code></a> 202<ul> 203<li><a href="#perf_hooks_histogram_disable"><code>histogram.disable()</code></a></li> 204<li><a href="#perf_hooks_histogram_enable"><code>histogram.enable()</code></a></li> 205<li><a href="#perf_hooks_cloning_an_intervalhistogram">Cloning an <code>IntervalHistogram</code></a></li> 206</ul> 207</li> 208<li><a href="#perf_hooks_class_recordablehistogram_extends_histogram">Class: <code>RecordableHistogram extends Histogram</code></a> 209<ul> 210<li><a href="#perf_hooks_histogram_record_val"><code>histogram.record(val)</code></a></li> 211<li><a href="#perf_hooks_histogram_recorddelta"><code>histogram.recordDelta()</code></a></li> 212</ul> 213</li> 214<li><a href="#perf_hooks_examples">Examples</a> 215<ul> 216<li><a href="#perf_hooks_measuring_the_duration_of_async_operations">Measuring the duration of async operations</a></li> 217<li><a href="#perf_hooks_measuring_how_long_it_takes_to_load_dependencies">Measuring how long it takes to load dependencies</a></li> 218</ul> 219</li> 220</ul> 221</li> 222</ul></details> 223 224 <div id="apicontent"> 225 <h2>Performance measurement APIs<span><a class="mark" href="#perf_hooks_performance_measurement_apis" id="perf_hooks_performance_measurement_apis">#</a></span></h2> 226 227<p></p><div class="api_stability api_stability_2"><a href="documentation.html#documentation_stability_index">Stability: 2</a> - Stable</div><p></p> 228<p><strong>Source Code:</strong> <a href="https://github.com/nodejs/node/blob/v14.19.1/lib/perf_hooks.js">lib/perf_hooks.js</a></p> 229<p>This module provides an implementation of a subset of the W3C 230<a href="https://w3c.github.io/perf-timing-primer/">Web Performance APIs</a> as well as additional APIs for 231Node.js-specific performance measurements.</p> 232<p>Node.js supports the following <a href="https://w3c.github.io/perf-timing-primer/">Web Performance APIs</a>:</p> 233<ul> 234<li><a href="https://www.w3.org/TR/hr-time-2">High Resolution Time</a></li> 235<li><a href="https://w3c.github.io/performance-timeline/">Performance Timeline</a></li> 236<li><a href="https://www.w3.org/TR/user-timing/">User Timing</a></li> 237</ul> 238<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>); 239 240<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> { 241 <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>); 242 performance.<span class="hljs-title function_">clearMarks</span>(); 243}); 244obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'measure'</span>] }); 245performance.<span class="hljs-title function_">measure</span>(<span class="hljs-string">'Start to Now'</span>); 246 247performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'A'</span>); 248<span class="hljs-title function_">doSomeLongRunningProcess</span>(<span class="hljs-function">() =></span> { 249 performance.<span class="hljs-title function_">measure</span>(<span class="hljs-string">'A to Now'</span>, <span class="hljs-string">'A'</span>); 250 251 performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'B'</span>); 252 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>); 253});</code></pre> 254<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> 255<div class="api_metadata"> 256<span>Added in: v8.5.0</span> 257</div> 258<p>An object that can be used to collect performance metrics from the current 259Node.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> 260<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> 261<div class="api_metadata"> 262<span>Added in: v8.5.0</span> 263</div> 264<ul> 265<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 266</ul> 267<p>If <code>name</code> is not provided, removes all <code>PerformanceMark</code> objects from the 268Performance Timeline. If <code>name</code> is provided, removes only the named mark.</p> 269<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> 270<div class="api_metadata"> 271<span>Added in: v14.10.0, v12.19.0</span> 272</div> 273<ul> 274<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 275<code>eventLoopUtilization()</code>.</li> 276<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 277<code>eventLoopUtilization()</code> prior to <code>utilization1</code>.</li> 278<li>Returns <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> 279<ul> 280<li><code>idle</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 281<li><code>active</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 282<li><code>utilization</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 283</ul> 284</li> 285</ul> 286<p>The <code>eventLoopUtilization()</code> method returns an object that contains the 287cumulative duration of time the event loop has been both idle and active as a 288high resolution milliseconds timer. The <code>utilization</code> value is the calculated 289Event Loop Utilization (ELU).</p> 290<p>If bootstrapping has not yet finished on the main thread the properties have 291the value of <code>0</code>. The ELU is immediately available on <a href="worker_threads.html#worker_threads_worker_threads">Worker threads</a> since 292bootstrap happens within the event loop.</p> 293<p>Both <code>utilization1</code> and <code>utilization2</code> are optional parameters.</p> 294<p>If <code>utilization1</code> is passed, then the delta between the current call's <code>active</code> 295and <code>idle</code> times, as well as the corresponding <code>utilization</code> value are 296calculated and returned (similar to <a href="process.html#process_process_hrtime_time"><code>process.hrtime()</code></a>).</p> 297<p>If <code>utilization1</code> and <code>utilization2</code> are both passed, then the delta is 298calculated between the two arguments. This is a convenience option because, 299unlike <a href="process.html#process_process_hrtime_time"><code>process.hrtime()</code></a>, calculating the ELU is more complex than a 300single subtraction.</p> 301<p>ELU is similar to CPU utilization, except that it only measures event loop 302statistics and not CPU usage. It represents the percentage of time the event 303loop has spent outside the event loop's event provider (e.g. <code>epoll_wait</code>). 304No other CPU idle time is taken into consideration. The following is an example 305of how a mostly idle process will have a high ELU.</p> 306<pre><code class="language-js"><span class="hljs-meta">'use strict'</span>; 307<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>; 308<span class="hljs-keyword">const</span> { spawnSync } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'child_process'</span>); 309 310<span class="hljs-title function_">setImmediate</span>(<span class="hljs-function">() =></span> { 311 <span class="hljs-keyword">const</span> elu = <span class="hljs-title function_">eventLoopUtilization</span>(); 312 <span class="hljs-title function_">spawnSync</span>(<span class="hljs-string">'sleep'</span>, [<span class="hljs-string">'5'</span>]); 313 <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>); 314});</code></pre> 315<p>Although the CPU is mostly idle while running this script, the value of 316<code>utilization</code> is <code>1</code>. This is because the call to 317<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> 318<p>Passing in a user-defined object instead of the result of a previous call to 319<code>eventLoopUtilization()</code> will lead to undefined behavior. The return values 320are not guaranteed to reflect any correct state of the event loop.</p> 321<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> 322<div class="api_metadata"> 323<span>Added in: v8.5.0</span> 324</div> 325<ul> 326<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 327</ul> 328<p>Creates a new <code>PerformanceMark</code> entry in the Performance Timeline. A 329<code>PerformanceMark</code> is a subclass of <code>PerformanceEntry</code> whose 330<code>performanceEntry.entryType</code> is always <code>'mark'</code>, and whose 331<code>performanceEntry.duration</code> is always <code>0</code>. Performance marks are used 332to mark specific significant moments in the Performance Timeline.</p> 333<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> 334<div class="api_metadata"> 335<details class="changelog"><summary>History</summary> 336<table> 337<tbody><tr><th>Version</th><th>Changes</th></tr> 338<tr><td>v14.0.0</td> 339<td><p>Make <code>startMark</code> and <code>endMark</code> parameters optional.</p></td></tr> 340<tr><td>v8.5.0</td> 341<td><p><span>Added in: v8.5.0</span></p></td></tr> 342</tbody></table> 343</details> 344</div> 345<ul> 346<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 347<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> 348<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> 349</ul> 350<p>Creates a new <code>PerformanceMeasure</code> entry in the Performance Timeline. A 351<code>PerformanceMeasure</code> is a subclass of <code>PerformanceEntry</code> whose 352<code>performanceEntry.entryType</code> is always <code>'measure'</code>, and whose 353<code>performanceEntry.duration</code> measures the number of milliseconds elapsed since 354<code>startMark</code> and <code>endMark</code>.</p> 355<p>The <code>startMark</code> argument may identify any <em>existing</em> <code>PerformanceMark</code> in the 356Performance Timeline, or <em>may</em> identify any of the timestamp properties 357provided by the <code>PerformanceNodeTiming</code> class. If the named <code>startMark</code> does 358not 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> 359<p>The optional <code>endMark</code> argument must identify any <em>existing</em> <code>PerformanceMark</code> 360in the Performance Timeline or any of the timestamp properties provided by the 361<code>PerformanceNodeTiming</code> class. <code>endMark</code> will be <code>performance.now()</code> 362if no parameter is passed, otherwise if the named <code>endMark</code> does not exist, an 363error will be thrown.</p> 364<h4><code>performance.nodeTiming</code><span><a class="mark" href="#perf_hooks_performance_nodetiming" id="perf_hooks_performance_nodetiming">#</a></span></h4> 365<div class="api_metadata"> 366<span>Added in: v8.5.0</span> 367</div> 368<ul> 369<li><a href="perf_hooks.html#perf_hooks_class_performancenodetiming" class="type"><PerformanceNodeTiming></a></li> 370</ul> 371<p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> 372<p>An instance of the <code>PerformanceNodeTiming</code> class that provides performance 373metrics for specific Node.js operational milestones.</p> 374<h4><code>performance.now()</code><span><a class="mark" href="#perf_hooks_performance_now" id="perf_hooks_performance_now">#</a></span></h4> 375<div class="api_metadata"> 376<span>Added in: v8.5.0</span> 377</div> 378<ul> 379<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 380</ul> 381<p>Returns the current high resolution millisecond timestamp, where 0 represents 382the start of the current <code>node</code> process.</p> 383<h4><code>performance.timeOrigin</code><span><a class="mark" href="#perf_hooks_performance_timeorigin" id="perf_hooks_performance_timeorigin">#</a></span></h4> 384<div class="api_metadata"> 385<span>Added in: v8.5.0</span> 386</div> 387<ul> 388<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 389</ul> 390<p>The <a href="https://w3c.github.io/hr-time/#dom-performance-timeorigin"><code>timeOrigin</code></a> specifies the high resolution millisecond timestamp at 391which the current <code>node</code> process began, measured in Unix time.</p> 392<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> 393<div class="api_metadata"> 394<span>Added in: v8.5.0</span> 395</div> 396<ul> 397<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li> 398</ul> 399<p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> 400<p>Wraps a function within a new function that measures the running time of the 401wrapped function. A <code>PerformanceObserver</code> must be subscribed to the <code>'function'</code> 402event type in order for the timing details to be accessed.</p> 403<pre><code class="language-js"><span class="hljs-keyword">const</span> { 404 performance, 405 <span class="hljs-title class_">PerformanceObserver</span> 406} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); 407 408<span class="hljs-keyword">function</span> <span class="hljs-title function_">someFunction</span>(<span class="hljs-params"></span>) { 409 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'hello world'</span>); 410} 411 412<span class="hljs-keyword">const</span> wrapped = performance.<span class="hljs-title function_">timerify</span>(someFunction); 413 414<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> { 415 <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>); 416 obs.<span class="hljs-title function_">disconnect</span>(); 417}); 418obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'function'</span>] }); 419 420<span class="hljs-comment">// A performance timeline entry will be created</span> 421<span class="hljs-title function_">wrapped</span>();</code></pre> 422</section><section><h3>Class: <code>PerformanceEntry</code><span><a class="mark" href="#perf_hooks_class_performanceentry" id="perf_hooks_class_performanceentry">#</a></span></h3> 423<div class="api_metadata"> 424<span>Added in: v8.5.0</span> 425</div> 426<h4><code>performanceEntry.duration</code><span><a class="mark" href="#perf_hooks_performanceentry_duration" id="perf_hooks_performanceentry_duration">#</a></span></h4> 427<div class="api_metadata"> 428<span>Added in: v8.5.0</span> 429</div> 430<ul> 431<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 432</ul> 433<p>The total number of milliseconds elapsed for this entry. This value will not 434be meaningful for all Performance Entry types.</p> 435<h4><code>performanceEntry.entryType</code><span><a class="mark" href="#perf_hooks_performanceentry_entrytype" id="perf_hooks_performanceentry_entrytype">#</a></span></h4> 436<div class="api_metadata"> 437<span>Added in: v8.5.0</span> 438</div> 439<ul> 440<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 441</ul> 442<p>The type of the performance entry. It may be one of:</p> 443<ul> 444<li><code>'node'</code> (Node.js only)</li> 445<li><code>'mark'</code> (available on the Web)</li> 446<li><code>'measure'</code> (available on the Web)</li> 447<li><code>'gc'</code> (Node.js only)</li> 448<li><code>'function'</code> (Node.js only)</li> 449<li><code>'http2'</code> (Node.js only)</li> 450<li><code>'http'</code> (Node.js only)</li> 451</ul> 452<h4><code>performanceEntry.flags</code><span><a class="mark" href="#perf_hooks_performanceentry_flags" id="perf_hooks_performanceentry_flags">#</a></span></h4> 453<div class="api_metadata"> 454<span>Added in: v13.9.0, v12.17.0</span> 455</div> 456<ul> 457<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 458</ul> 459<p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> 460<p>When <code>performanceEntry.entryType</code> is equal to <code>'gc'</code>, the <code>performance.flags</code> 461property contains additional information about garbage collection operation. 462The value may be one of:</p> 463<ul> 464<li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_NO</code></li> 465<li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_CONSTRUCT_RETAINED</code></li> 466<li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_FORCED</code></li> 467<li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SYNCHRONOUS_PHANTOM_PROCESSING</code></li> 468<li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_AVAILABLE_GARBAGE</code></li> 469<li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_ALL_EXTERNAL_MEMORY</code></li> 470<li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_FLAGS_SCHEDULE_IDLE</code></li> 471</ul> 472<h4><code>performanceEntry.name</code><span><a class="mark" href="#perf_hooks_performanceentry_name" id="perf_hooks_performanceentry_name">#</a></span></h4> 473<div class="api_metadata"> 474<span>Added in: v8.5.0</span> 475</div> 476<ul> 477<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 478</ul> 479<p>The name of the performance entry.</p> 480<h4><code>performanceEntry.kind</code><span><a class="mark" href="#perf_hooks_performanceentry_kind" id="perf_hooks_performanceentry_kind">#</a></span></h4> 481<div class="api_metadata"> 482<span>Added in: v8.5.0</span> 483</div> 484<ul> 485<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 486</ul> 487<p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> 488<p>When <code>performanceEntry.entryType</code> is equal to <code>'gc'</code>, the <code>performance.kind</code> 489property identifies the type of garbage collection operation that occurred. 490The value may be one of:</p> 491<ul> 492<li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_MAJOR</code></li> 493<li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_MINOR</code></li> 494<li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_INCREMENTAL</code></li> 495<li><code>perf_hooks.constants.NODE_PERFORMANCE_GC_WEAKCB</code></li> 496</ul> 497<h4><code>performanceEntry.startTime</code><span><a class="mark" href="#perf_hooks_performanceentry_starttime" id="perf_hooks_performanceentry_starttime">#</a></span></h4> 498<div class="api_metadata"> 499<span>Added in: v8.5.0</span> 500</div> 501<ul> 502<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 503</ul> 504<p>The high resolution millisecond timestamp marking the starting time of the 505Performance Entry.</p> 506</section><section><h3>Class: <code>PerformanceNodeTiming</code><span><a class="mark" href="#perf_hooks_class_performancenodetiming" id="perf_hooks_class_performancenodetiming">#</a></span></h3> 507<div class="api_metadata"> 508<span>Added in: v8.5.0</span> 509</div> 510<ul> 511<li>Extends: <a href="perf_hooks.html#perf_hooks_class_performanceentry" class="type"><PerformanceEntry></a></li> 512</ul> 513<p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> 514<p>Provides timing details for Node.js itself. The constructor of this class 515is not exposed to users.</p> 516<h4><code>performanceNodeTiming.bootstrapComplete</code><span><a class="mark" href="#perf_hooks_performancenodetiming_bootstrapcomplete" id="perf_hooks_performancenodetiming_bootstrapcomplete">#</a></span></h4> 517<div class="api_metadata"> 518<span>Added in: v8.5.0</span> 519</div> 520<ul> 521<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 522</ul> 523<p>The high resolution millisecond timestamp at which the Node.js process 524completed bootstrapping. If bootstrapping has not yet finished, the property 525has the value of -1.</p> 526<h4><code>performanceNodeTiming.environment</code><span><a class="mark" href="#perf_hooks_performancenodetiming_environment" id="perf_hooks_performancenodetiming_environment">#</a></span></h4> 527<div class="api_metadata"> 528<span>Added in: v8.5.0</span> 529</div> 530<ul> 531<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 532</ul> 533<p>The high resolution millisecond timestamp at which the Node.js environment was 534initialized.</p> 535<h4><code>performanceNodeTiming.idleTime</code><span><a class="mark" href="#perf_hooks_performancenodetiming_idletime" id="perf_hooks_performancenodetiming_idletime">#</a></span></h4> 536<div class="api_metadata"> 537<span>Added in: v14.10.0, v12.19.0</span> 538</div> 539<ul> 540<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 541</ul> 542<p>The high resolution millisecond timestamp of the amount of time the event loop 543has been idle within the event loop's event provider (e.g. <code>epoll_wait</code>). This 544does not take CPU usage into consideration. If the event loop has not yet 545started (e.g., in the first tick of the main script), the property has the 546value of 0.</p> 547<h4><code>performanceNodeTiming.loopExit</code><span><a class="mark" href="#perf_hooks_performancenodetiming_loopexit" id="perf_hooks_performancenodetiming_loopexit">#</a></span></h4> 548<div class="api_metadata"> 549<span>Added in: v8.5.0</span> 550</div> 551<ul> 552<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 553</ul> 554<p>The high resolution millisecond timestamp at which the Node.js event loop 555exited. If the event loop has not yet exited, the property has the value of -1. 556It 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> 557<h4><code>performanceNodeTiming.loopStart</code><span><a class="mark" href="#perf_hooks_performancenodetiming_loopstart" id="perf_hooks_performancenodetiming_loopstart">#</a></span></h4> 558<div class="api_metadata"> 559<span>Added in: v8.5.0</span> 560</div> 561<ul> 562<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 563</ul> 564<p>The high resolution millisecond timestamp at which the Node.js event loop 565started. If the event loop has not yet started (e.g., in the first tick of the 566main script), the property has the value of -1.</p> 567<h4><code>performanceNodeTiming.nodeStart</code><span><a class="mark" href="#perf_hooks_performancenodetiming_nodestart" id="perf_hooks_performancenodetiming_nodestart">#</a></span></h4> 568<div class="api_metadata"> 569<span>Added in: v8.5.0</span> 570</div> 571<ul> 572<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 573</ul> 574<p>The high resolution millisecond timestamp at which the Node.js process was 575initialized.</p> 576<h4><code>performanceNodeTiming.v8Start</code><span><a class="mark" href="#perf_hooks_performancenodetiming_v8start" id="perf_hooks_performancenodetiming_v8start">#</a></span></h4> 577<div class="api_metadata"> 578<span>Added in: v8.5.0</span> 579</div> 580<ul> 581<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 582</ul> 583<p>The high resolution millisecond timestamp at which the V8 platform was 584initialized.</p> 585</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> 586<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> 587<div class="api_metadata"> 588<span>Added in: v8.5.0</span> 589</div> 590<ul> 591<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> 592<ul> 593<li><code>list</code> <a href="perf_hooks.html#perf_hooks_class_performanceobserverentrylist" class="type"><PerformanceObserverEntryList></a></li> 594<li><code>observer</code> <a href="perf_hooks.html#perf_hooks_class_perf_hooks_performanceobserver" class="type"><PerformanceObserver></a></li> 595</ul> 596</li> 597</ul> 598<p><code>PerformanceObserver</code> objects provide notifications when new 599<code>PerformanceEntry</code> instances have been added to the Performance Timeline.</p> 600<pre><code class="language-js"><span class="hljs-keyword">const</span> { 601 performance, 602 <span class="hljs-title class_">PerformanceObserver</span> 603} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); 604 605<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> { 606 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(list.<span class="hljs-title function_">getEntries</span>()); 607 observer.<span class="hljs-title function_">disconnect</span>(); 608}); 609obs.<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> }); 610 611performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'test'</span>);</code></pre> 612<p>Because <code>PerformanceObserver</code> instances introduce their own additional 613performance overhead, instances should not be left subscribed to notifications 614indefinitely. Users should disconnect observers as soon as they are no 615longer needed.</p> 616<p>The <code>callback</code> is invoked when a <code>PerformanceObserver</code> is 617notified about new <code>PerformanceEntry</code> instances. The callback receives a 618<code>PerformanceObserverEntryList</code> instance and a reference to the 619<code>PerformanceObserver</code>.</p> 620<h4><code>performanceObserver.disconnect()</code><span><a class="mark" href="#perf_hooks_performanceobserver_disconnect" id="perf_hooks_performanceobserver_disconnect">#</a></span></h4> 621<div class="api_metadata"> 622<span>Added in: v8.5.0</span> 623</div> 624<p>Disconnects the <code>PerformanceObserver</code> instance from all notifications.</p> 625<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> 626<div class="api_metadata"> 627<span>Added in: v8.5.0</span> 628</div> 629<ul> 630<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> 631<ul> 632<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 633<code>PerformanceEntry</code> instances the observer is interested in. If not 634provided an error will be thrown.</li> 635<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 636called using <code>setImmediate()</code> and multiple <code>PerformanceEntry</code> instance 637notifications will be buffered internally. If <code>false</code>, notifications will 638be immediate and synchronous. <strong>Default:</strong> <code>false</code>.</li> 639</ul> 640</li> 641</ul> 642<p>Subscribes the <code>PerformanceObserver</code> instance to notifications of new 643<code>PerformanceEntry</code> instances identified by <code>options.entryTypes</code>.</p> 644<p>When <code>options.buffered</code> is <code>false</code>, the <code>callback</code> will be invoked once for 645every <code>PerformanceEntry</code> instance:</p> 646<pre><code class="language-js"><span class="hljs-keyword">const</span> { 647 performance, 648 <span class="hljs-title class_">PerformanceObserver</span> 649} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); 650 651<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> { 652 <span class="hljs-comment">// Called three times synchronously. `list` contains one item.</span> 653}); 654obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'mark'</span>] }); 655 656<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++) 657 performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">`test<span class="hljs-subst">${n}</span>`</span>);</code></pre> 658<pre><code class="language-js"><span class="hljs-keyword">const</span> { 659 performance, 660 <span class="hljs-title class_">PerformanceObserver</span> 661} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); 662 663<span class="hljs-keyword">const</span> obs = <span class="hljs-keyword">new</span> <span class="hljs-title class_">PerformanceObserver</span>(<span class="hljs-function">(<span class="hljs-params">list, observer</span>) =></span> { 664 <span class="hljs-comment">// Called once. `list` contains three items.</span> 665}); 666obs.<span class="hljs-title function_">observe</span>({ <span class="hljs-attr">entryTypes</span>: [<span class="hljs-string">'mark'</span>], <span class="hljs-attr">buffered</span>: <span class="hljs-literal">true</span> }); 667 668<span class="hljs-keyword">for</span> (<span class="hljs-keyword">let</span> n = <span class="hljs-number">0</span>; n < <span class="hljs-number">3</span>; n++) 669 performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">`test<span class="hljs-subst">${n}</span>`</span>);</code></pre> 670</section><section><h3>Class: <code>PerformanceObserverEntryList</code><span><a class="mark" href="#perf_hooks_class_performanceobserverentrylist" id="perf_hooks_class_performanceobserverentrylist">#</a></span></h3> 671<div class="api_metadata"> 672<span>Added in: v8.5.0</span> 673</div> 674<p>The <code>PerformanceObserverEntryList</code> class is used to provide access to the 675<code>PerformanceEntry</code> instances passed to a <code>PerformanceObserver</code>. 676The constructor of this class is not exposed to users.</p> 677<h4><code>performanceObserverEntryList.getEntries()</code><span><a class="mark" href="#perf_hooks_performanceobserverentrylist_getentries" id="perf_hooks_performanceobserverentrylist_getentries">#</a></span></h4> 678<div class="api_metadata"> 679<span>Added in: v8.5.0</span> 680</div> 681<ul> 682<li>Returns: <a href="perf_hooks.html#perf_hooks_class_performanceentry" class="type"><PerformanceEntry[]></a></li> 683</ul> 684<p>Returns a list of <code>PerformanceEntry</code> objects in chronological order 685with respect to <code>performanceEntry.startTime</code>.</p> 686<pre><code class="language-js"><span class="hljs-keyword">const</span> { 687 performance, 688 <span class="hljs-title class_">PerformanceObserver</span> 689} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); 690 691<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> { 692 <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(perfObserverList.<span class="hljs-title function_">getEntries</span>()); 693 <span class="hljs-comment">/** 694 * [ 695 * PerformanceEntry { 696 * name: 'test', 697 * entryType: 'mark', 698 * startTime: 81.465639, 699 * duration: 0 700 * }, 701 * PerformanceEntry { 702 * name: 'meow', 703 * entryType: 'mark', 704 * startTime: 81.860064, 705 * duration: 0 706 * } 707 * ] 708 */</span> 709 observer.<span class="hljs-title function_">disconnect</span>(); 710}); 711obs.<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> }); 712 713performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'test'</span>); 714performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'meow'</span>);</code></pre> 715<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> 716<div class="api_metadata"> 717<span>Added in: v8.5.0</span> 718</div> 719<ul> 720<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 721<li><code>type</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 722<li>Returns: <a href="perf_hooks.html#perf_hooks_class_performanceentry" class="type"><PerformanceEntry[]></a></li> 723</ul> 724<p>Returns a list of <code>PerformanceEntry</code> objects in chronological order 725with respect to <code>performanceEntry.startTime</code> whose <code>performanceEntry.name</code> is 726equal to <code>name</code>, and optionally, whose <code>performanceEntry.entryType</code> is equal to 727<code>type</code>.</p> 728<pre><code class="language-js"><span class="hljs-keyword">const</span> { 729 performance, 730 <span class="hljs-title class_">PerformanceObserver</span> 731} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); 732 733<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> { 734 <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>)); 735 <span class="hljs-comment">/** 736 * [ 737 * PerformanceEntry { 738 * name: 'meow', 739 * entryType: 'mark', 740 * startTime: 98.545991, 741 * duration: 0 742 * } 743 * ] 744 */</span> 745 <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> 746 747 <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>)); 748 <span class="hljs-comment">/** 749 * [ 750 * PerformanceEntry { 751 * name: 'test', 752 * entryType: 'mark', 753 * startTime: 63.518931, 754 * duration: 0 755 * } 756 * ] 757 */</span> 758 <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> 759 observer.<span class="hljs-title function_">disconnect</span>(); 760}); 761obs.<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> }); 762 763performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'test'</span>); 764performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'meow'</span>);</code></pre> 765<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> 766<div class="api_metadata"> 767<span>Added in: v8.5.0</span> 768</div> 769<ul> 770<li><code>type</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 771<li>Returns: <a href="perf_hooks.html#perf_hooks_class_performanceentry" class="type"><PerformanceEntry[]></a></li> 772</ul> 773<p>Returns a list of <code>PerformanceEntry</code> objects in chronological order 774with respect to <code>performanceEntry.startTime</code> whose <code>performanceEntry.entryType</code> 775is equal to <code>type</code>.</p> 776<pre><code class="language-js"><span class="hljs-keyword">const</span> { 777 performance, 778 <span class="hljs-title class_">PerformanceObserver</span> 779} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); 780 781<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> { 782 <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>)); 783 <span class="hljs-comment">/** 784 * [ 785 * PerformanceEntry { 786 * name: 'test', 787 * entryType: 'mark', 788 * startTime: 55.897834, 789 * duration: 0 790 * }, 791 * PerformanceEntry { 792 * name: 'meow', 793 * entryType: 'mark', 794 * startTime: 56.350146, 795 * duration: 0 796 * } 797 * ] 798 */</span> 799 observer.<span class="hljs-title function_">disconnect</span>(); 800}); 801obs.<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> }); 802 803performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'test'</span>); 804performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">'meow'</span>);</code></pre> 805</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> 806<div class="api_metadata"> 807<span>Added in: v14.18.0</span> 808</div> 809<ul> 810<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> 811<ul> 812<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 813value greater than 0. <strong>Defaults</strong>: <code>1</code>.</li> 814<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 815value greater than <code>min</code>. <strong>Defaults</strong>: <code>Number.MAX_SAFE_INTEGER</code>.</li> 816<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 817<code>1</code> and <code>5</code>. <strong>Defaults</strong>: <code>3</code>.</li> 818</ul> 819</li> 820<li>Returns <a href="perf_hooks.html#perf_hooks_class_recordablehistogram_extends_histogram" class="type"><RecordableHistogram></a></li> 821</ul> 822<p>Returns a <a href="perf_hooks.html#perf_hooks_class_recordablehistogram_extends_histogram" class="type"><RecordableHistogram></a>.</p> 823</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> 824<div class="api_metadata"> 825<span>Added in: v11.10.0</span> 826</div> 827<ul> 828<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> 829<ul> 830<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 831than zero. <strong>Default:</strong> <code>10</code>.</li> 832</ul> 833</li> 834<li>Returns: <a href="perf_hooks.html#perf_hooks_class_intervalhistogram_extends_histogram" class="type"><IntervalHistogram></a></li> 835</ul> 836<p><em>This property is an extension by Node.js. It is not available in Web browsers.</em></p> 837<p>Creates an <code>IntervalHistogram</code> object that samples and reports the event loop 838delay over time. The delays will be reported in nanoseconds.</p> 839<p>Using a timer to detect approximate event loop delay works because the 840execution of timers is tied specifically to the lifecycle of the libuv 841event loop. That is, a delay in the loop will cause a delay in the execution 842of the timer, and those delays are specifically what this API is intended to 843detect.</p> 844<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>); 845<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> }); 846h.<span class="hljs-title function_">enable</span>(); 847<span class="hljs-comment">// Do something.</span> 848h.<span class="hljs-title function_">disable</span>(); 849<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(h.<span class="hljs-property">min</span>); 850<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(h.<span class="hljs-property">max</span>); 851<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(h.<span class="hljs-property">mean</span>); 852<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(h.<span class="hljs-property">stddev</span>); 853<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(h.<span class="hljs-property">percentiles</span>); 854<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>)); 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">99</span>));</code></pre> 856</section><section><h3>Class: <code>Histogram</code><span><a class="mark" href="#perf_hooks_class_histogram" id="perf_hooks_class_histogram">#</a></span></h3> 857<div class="api_metadata"> 858<span>Added in: v11.10.0</span> 859</div> 860<h4><code>histogram.exceeds</code><span><a class="mark" href="#perf_hooks_histogram_exceeds" id="perf_hooks_histogram_exceeds">#</a></span></h4> 861<div class="api_metadata"> 862<span>Added in: v11.10.0</span> 863</div> 864<ul> 865<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 866</ul> 867<p>The number of times the event loop delay exceeded the maximum 1 hour event 868loop delay threshold.</p> 869<h4><code>histogram.max</code><span><a class="mark" href="#perf_hooks_histogram_max" id="perf_hooks_histogram_max">#</a></span></h4> 870<div class="api_metadata"> 871<span>Added in: v11.10.0</span> 872</div> 873<ul> 874<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 875</ul> 876<p>The maximum recorded event loop delay.</p> 877<h4><code>histogram.mean</code><span><a class="mark" href="#perf_hooks_histogram_mean" id="perf_hooks_histogram_mean">#</a></span></h4> 878<div class="api_metadata"> 879<span>Added in: v11.10.0</span> 880</div> 881<ul> 882<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 883</ul> 884<p>The mean of the recorded event loop delays.</p> 885<h4><code>histogram.min</code><span><a class="mark" href="#perf_hooks_histogram_min" id="perf_hooks_histogram_min">#</a></span></h4> 886<div class="api_metadata"> 887<span>Added in: v11.10.0</span> 888</div> 889<ul> 890<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 891</ul> 892<p>The minimum recorded event loop delay.</p> 893<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> 894<div class="api_metadata"> 895<span>Added in: v11.10.0</span> 896</div> 897<ul> 898<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> 899<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 900</ul> 901<p>Returns the value at the given percentile.</p> 902<h4><code>histogram.percentiles</code><span><a class="mark" href="#perf_hooks_histogram_percentiles" id="perf_hooks_histogram_percentiles">#</a></span></h4> 903<div class="api_metadata"> 904<span>Added in: v11.10.0</span> 905</div> 906<ul> 907<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map" class="type"><Map></a></li> 908</ul> 909<p>Returns a <code>Map</code> object detailing the accumulated percentile distribution.</p> 910<h4><code>histogram.reset()</code><span><a class="mark" href="#perf_hooks_histogram_reset" id="perf_hooks_histogram_reset">#</a></span></h4> 911<div class="api_metadata"> 912<span>Added in: v11.10.0</span> 913</div> 914<p>Resets the collected histogram data.</p> 915<h4><code>histogram.stddev</code><span><a class="mark" href="#perf_hooks_histogram_stddev" id="perf_hooks_histogram_stddev">#</a></span></h4> 916<div class="api_metadata"> 917<span>Added in: v11.10.0</span> 918</div> 919<ul> 920<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> 921</ul> 922<p>The standard deviation of the recorded event loop delays.</p> 923</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> 924<p>A <code>Histogram</code> that is periodically updated on a given interval.</p> 925<h4><code>histogram.disable()</code><span><a class="mark" href="#perf_hooks_histogram_disable" id="perf_hooks_histogram_disable">#</a></span></h4> 926<div class="api_metadata"> 927<span>Added in: v11.10.0</span> 928</div> 929<ul> 930<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> 931</ul> 932<p>Disables the update interval timer. Returns <code>true</code> if the timer was 933stopped, <code>false</code> if it was already stopped.</p> 934<h4><code>histogram.enable()</code><span><a class="mark" href="#perf_hooks_histogram_enable" id="perf_hooks_histogram_enable">#</a></span></h4> 935<div class="api_metadata"> 936<span>Added in: v11.10.0</span> 937</div> 938<ul> 939<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li> 940</ul> 941<p>Enables the update interval timer. Returns <code>true</code> if the timer was 942started, <code>false</code> if it was already started.</p> 943<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> 944<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 945end, the histogram is cloned as a plain <a href="perf_hooks.html#perf_hooks_class_histogram" class="type"><Histogram></a> object that does not 946implement the <code>enable()</code> and <code>disable()</code> methods.</p> 947</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> 948<div class="api_metadata"> 949<span>Added in: v14.18.0</span> 950</div> 951<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> 952<div class="api_metadata"> 953<span>Added in: v14.18.0</span> 954</div> 955<ul> 956<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> 957</ul> 958<h4><code>histogram.recordDelta()</code><span><a class="mark" href="#perf_hooks_histogram_recorddelta" id="perf_hooks_histogram_recorddelta">#</a></span></h4> 959<div class="api_metadata"> 960<span>Added in: v14.18.0</span> 961</div> 962<p>Calculates the amount of time (in nanoseconds) that has passed since the 963previous call to <code>recordDelta()</code> and records that amount in the histogram.</p> 964</section><section><h3>Examples<span><a class="mark" href="#perf_hooks_examples" id="perf_hooks_examples">#</a></span></h3> 965<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> 966<p>The following example uses the <a href="async_hooks.html">Async Hooks</a> and Performance APIs to measure 967the actual duration of a Timeout operation (including the amount of time it took 968to execute the callback).</p> 969<pre><code class="language-js"><span class="hljs-meta">'use strict'</span>; 970<span class="hljs-keyword">const</span> async_hooks = <span class="hljs-built_in">require</span>(<span class="hljs-string">'async_hooks'</span>); 971<span class="hljs-keyword">const</span> { 972 performance, 973 <span class="hljs-title class_">PerformanceObserver</span> 974} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); 975 976<span class="hljs-keyword">const</span> set = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Set</span>(); 977<span class="hljs-keyword">const</span> hook = async_hooks.<span class="hljs-title function_">createHook</span>({ 978 <span class="hljs-title function_">init</span>(<span class="hljs-params">id, type</span>) { 979 <span class="hljs-keyword">if</span> (type === <span class="hljs-string">'Timeout'</span>) { 980 performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">`Timeout-<span class="hljs-subst">${id}</span>-Init`</span>); 981 set.<span class="hljs-title function_">add</span>(id); 982 } 983 }, 984 <span class="hljs-title function_">destroy</span>(<span class="hljs-params">id</span>) { 985 <span class="hljs-keyword">if</span> (set.<span class="hljs-title function_">has</span>(id)) { 986 set.<span class="hljs-title function_">delete</span>(id); 987 performance.<span class="hljs-title function_">mark</span>(<span class="hljs-string">`Timeout-<span class="hljs-subst">${id}</span>-Destroy`</span>); 988 performance.<span class="hljs-title function_">measure</span>(<span class="hljs-string">`Timeout-<span class="hljs-subst">${id}</span>`</span>, 989 <span class="hljs-string">`Timeout-<span class="hljs-subst">${id}</span>-Init`</span>, 990 <span class="hljs-string">`Timeout-<span class="hljs-subst">${id}</span>-Destroy`</span>); 991 } 992 } 993}); 994hook.<span class="hljs-title function_">enable</span>(); 995 996<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> { 997 <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>]); 998 performance.<span class="hljs-title function_">clearMarks</span>(); 999 observer.<span class="hljs-title function_">disconnect</span>(); 1000}); 1001obs.<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> }); 1002 1003<span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> {}, <span class="hljs-number">1000</span>);</code></pre> 1004<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> 1005<p>The following example measures the duration of <code>require()</code> operations to load 1006dependencies:</p> 1007<!-- eslint-disable no-global-assign --> 1008<pre><code class="language-js"><span class="hljs-meta">'use strict'</span>; 1009<span class="hljs-keyword">const</span> { 1010 performance, 1011 <span class="hljs-title class_">PerformanceObserver</span> 1012} = <span class="hljs-built_in">require</span>(<span class="hljs-string">'perf_hooks'</span>); 1013<span class="hljs-keyword">const</span> mod = <span class="hljs-built_in">require</span>(<span class="hljs-string">'module'</span>); 1014 1015<span class="hljs-comment">// Monkey patch the require function</span> 1016mod.<span class="hljs-property">Module</span>.<span class="hljs-property"><span class="hljs-keyword">prototype</span></span>.<span class="hljs-property">require</span> = 1017 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>); 1018<span class="hljs-built_in">require</span> = performance.<span class="hljs-title function_">timerify</span>(<span class="hljs-built_in">require</span>); 1019 1020<span class="hljs-comment">// Activate the observer</span> 1021<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> { 1022 <span class="hljs-keyword">const</span> entries = list.<span class="hljs-title function_">getEntries</span>(); 1023 entries.<span class="hljs-title function_">forEach</span>(<span class="hljs-function">(<span class="hljs-params">entry</span>) =></span> { 1024 <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>); 1025 }); 1026 obs.<span class="hljs-title function_">disconnect</span>(); 1027}); 1028obs.<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> }); 1029 1030<span class="hljs-built_in">require</span>(<span class="hljs-string">'some-module'</span>);</code></pre></section> 1031 <!-- API END --> 1032 </div> 1033 </div> 1034 </div> 1035 <script> 1036 'use strict'; 1037 { 1038 const kCustomPreference = 'customDarkTheme'; 1039 const userSettings = sessionStorage.getItem(kCustomPreference); 1040 const themeToggleButton = document.getElementById('theme-toggle-btn'); 1041 if (userSettings === null && window.matchMedia) { 1042 const mq = window.matchMedia('(prefers-color-scheme: dark)'); 1043 if ('onchange' in mq) { 1044 function mqChangeListener(e) { 1045 document.body.classList.toggle('dark-mode', e.matches); 1046 } 1047 mq.addEventListener('change', mqChangeListener); 1048 if (themeToggleButton) { 1049 themeToggleButton.addEventListener('click', function() { 1050 mq.removeEventListener('change', mqChangeListener); 1051 }, { once: true }); 1052 } 1053 } 1054 if (mq.matches) { 1055 document.body.classList.add('dark-mode'); 1056 } 1057 } else if (userSettings === 'true') { 1058 document.body.classList.add('dark-mode'); 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