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+---
+title: Performance Timeline
+slug: Web/API/Performance_Timeline
+translation_of: Web/API/Performance_Timeline
+---
+<div>{{DefaultAPISidebar("Performance Timeline API")}}</div>
+
+<p>The <strong>Performance Timeline</strong> API defines extensions to the {{domxref("Performance")}} interface to support client-side latency measurements within applications. The extensions provide interfaces to retrieve {{domxref("PerformanceEntry","performance entry metrics", '', 'true')}} based on specific filter criteria. The standard also includes interfaces that allow an application to define <em>{{anch("Performance_Observers","performance observer", '', 'true')}}</em> callbacks that are notified when specific performance events are added to the browser's <em>performance timeline</em>.</p>
+
+<p>This document provides an overview of the standard's interfaces. For more details about the interfaces, see the reference pages and <a href="/Web/API/Performance_Timeline/Using_Performance_Timeline">Using Performance Timeline</a>.</p>
+
+<h2 id="Performance_extensions">Performance extensions</h2>
+
+<p>The Performance Timeline API extends the {{domxref("Performance")}} interface with three methods that provide different mechanisms to get a set of {{domxref("PerformanceEntry","performance records (metrics)")}}, depending on the specified filter criteria. The methods are:</p>
+
+<dl>
+ <dt>{{domxref("Performance.getEntries","getEntries()")}}</dt>
+ <dd>Returns all recorded {{domxref("PerformanceEntry","performance entries")}} or, optionally, the entries based on the specified {{domxref("PerformanceEntry.name","name")}}, {{domxref("PerformanceEntry.entryType","performance type")}} and/or the {{domxref("PerformanceEntry.initiatorType","initiatorType")}} (such as an HTML element).</dd>
+ <dt>{{domxref("Performance.getEntriesByName","getEntriesByName()")}}</dt>
+ <dd>Returns the recorded {{domxref("PerformanceEntry","performance entries")}} based on the specified {{domxref("PerformanceEntry.name","name")}} and optionally the {{domxref("PerformanceEntry.entryType","performance type")}}.</dd>
+ <dt>{{domxref("Performance.getEntriesByType","getEntriesByType()")}}</dt>
+ <dd>Returns the recorded {{domxref("PerformanceEntry","performance entries")}} based on the specified {{domxref("PerformanceEntry.entryType","performance type")}}.</dd>
+</dl>
+
+<h2 id="PerformanceEntry_interface">PerformanceEntry interface</h2>
+
+<p>The {{domxref("PerformanceEntry")}} interface encapsulates a single <em>performance entry</em> — that is, a single data point or metric in the <em>performance timeline</em>. This interface has the following four properties, and these properties are extended (with additional constraints) by other interfaces (such as {{domxref("PerformanceMark")}}):</p>
+
+<dl>
+ <dt>{{domxref("PerformanceEntry.name","name")}}</dt>
+ <dd>The name of the performance entry when the metric was created.</dd>
+ <dt>{{domxref("PerformanceEntry.entryType","entryType")}}</dt>
+ <dd>The type of performance metric (for example, "<code>mark</code>").</dd>
+ <dt>{{domxref("PerformanceEntry.startTime","startTime")}}</dt>
+ <dd>A {{domxref("DOMHighResTimeStamp","high resolution timestamp")}} representing the starting time for the performance entry.</dd>
+ <dt>{{domxref("PerformanceEntry.duration","duration")}}</dt>
+ <dd>A {{domxref("DOMHighResTimeStamp","high resolution timestamp", '', 'true')}} representing the time value of the duration of the performance event. (Some performance {{domxref("PerformanceEntry.entryType","entry types", '', 'true')}} have no concept of <em>duration</em> and this value is set to <code>'0'</code> for such types.)</dd>
+</dl>
+
+<p>This interface includes a {{domxref("PerformanceEntry.toJSON","toJSON()")}} method that returns the serialization of the {{domxref("PerformanceEntry")}} object. The serialization is specific to the performance entry's {{domxref("PerformanceEntry.entryType","type")}}.</p>
+
+<h2 id="Performance_observers">Performance observers</h2>
+
+<p>{{SeeCompatTable}}</p>
+
+<p>The <em>performance observer</em> interfaces allow an application to register an <em>observer</em> for specific performance event types, and when one of those event types is recorded, the application is <em>notified</em> of the event via the observer's callback function that was specified when the observer was created.</p>
+
+<p>When the observer (callback) is invoked, the callback's parameters include a <em>{{domxref("PerformanceObserverEntryList","performance observer entry list")}}</em> that contains only <em>observed</em> {{domxref("PerformanceEntry","performance entries")}}. That is, the list contains entries only for the event types that were specified when the observer's {{domxref("PerformanceObserver.observe","observe()")}} method was invoked. The {{domxref("PerformanceObserverEntryList","performance observer entry list")}} interface has the same three <code>getEntries*()</code> methods as the {{domxref("Performance")}} interface. However, note there is one key difference with these methods; the {{domxref("PerformanceObserverEntryList","performance observer entry list")}} versions are used to retrieve <em>observed</em> performance entries within the observer callback.</p>
+
+<p>Besides the {{domxref("PerformanceObserver","PerformanceObserver's")}} interface's {{domxref("PerformanceObserver.observe","observe()")}} method (which is used to register the {{domxref("PerformanceEntry.entryType","entry types")}} to <em>observe</em>), the {{domxref("PerformanceObserver")}} interface also has a {{domxref("PerformanceObserver.disconnect","disconnect()")}} method that stops an observer from receiving further events.</p>
+
+<p class="note">Performance observers were added to the <code>Level 2</code> version of the standard and were not widely implemented.</p>
+
+<h2 id="实现状态">实现状态</h2>
+
+<p>A summary of the interfaces' implementation status is provided below, including a link to more detailed information.</p>
+
+<ul>
+ <li>Performance interface extensions: As shown in the {{domxref("Performance")}} interface's <a href="/Web/API/Performance#Browser_compatibility">Browser Compatibility</a> table, most of these interfaces are broadly implemented by desktop browsers and have less support on mobile devices.</li>
+ <li>PerformanceEntry: As shown in the {{domxref("PerformanceEntry")}} interface's <a href="/Web/API/PerformanceEntry#Browser_compatibility">Browser Compatibility</a> table, most of these interfaces are broadly implemented by desktop browsers and have less support on mobile devices.</li>
+ <li>Performance Observers {{experimental_inline}}: As shown in the {{domxref("PerformanceObserver")}} interface's <a href="/Web/API/PerformanceObserver#Browser_compatibility">Browser Compatibility</a> table, this interface has no shipping implementations.</li>
+</ul>
+
+<p>To test your browser's support for these interfaces, run the <code><a href="http://mdn.github.io/web-performance/perf-api-support.html">perf-api-support</a></code> application.</p>
+
+<h2 id="参见">参见</h2>
+
+<ul>
+ <li><a href="http://siusin.github.io/perf-timing-primer/">A Primer for Web Performance Timing APIs</a></li>
+</ul>