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---
title: performance.now()
slug: Web/API/Performance/now
translation_of: Web/API/Performance/now
---
<div>{{APIRef("High Resolution Timing")}}</div>
<p>O método <code><strong>performance.now()</strong></code> retorna {{domxref("DOMHighResTimeStamp")}}, medido em milisegundos, com precisão de cinco milésimos de milissegundo (5 microsegundos).</p>
<p>O valor retornado representa o tempo decorrido desde o <strong>time origin </strong>(the {{domxref("PerformanceTiming.navigationStart")}} property). Em um web worker, o tempo inicial é o momento em que o contexto da execução(e.g. thread ou processo) é criado. Em uma janela, é o tempo em que o usuário iniciou a navegação neste documento. Tenha em mente que:</p>
<ul>
<li>Em workers dedicados criados do {{domxref("Window")}}, o valor neste worker será inferior a <code>performance.now()</code> na window que gerou este worker. Normalmente é o mesmo que <code>t0</code> no contexto principal, mas esse valor foi alterado.</li>
<li>Em shared workers ou service workers, o valor do worker pode ser maior em relação ao contexto principal poir estas janelas podem ser criadas depois destes workers.</li>
</ul>
<h2 id="Sintaxe">Sintaxe</h2>
<pre class="syntaxbox"><em>t</em> = performance.now();</pre>
<h2 id="Exemplo">Exemplo</h2>
<pre class="brush: js">var t0 = performance.now();
doSomething();
var t1 = performance.now();
console.log("Call to doSomething took " + (t1 - t0) + " milliseconds.");
</pre>
<p>Unlike other timing data available to JavaScript (for example <a href="/en-US/docs/JavaScript/Reference/Global_Objects/Date/now"><code>Date.now</code></a>), the timestamps returned by <code>Performance.now()</code> are not limited to one-millisecond resolution. Instead, they represent times as floating-point numbers with up to microsecond precision.</p>
<p>Also unlike <code>Date.now()</code>, the values returned by <code>Performance.now() </code>always increase at a constant rate, independent of the system clock (which might be adjusted manually or skewed by software like NTP). Otherwise, <code>performance.timing.navigationStart + performance.now() </code>will be approximately equal to<code> Date.now()</code>.</p>
<h2 id="Especificações">Especificações</h2>
<table class="standard-table">
<tbody>
<tr>
<th scope="col">Specification</th>
<th scope="col">Status</th>
<th scope="col">Comment</th>
</tr>
<tr>
<td>{{SpecName('Highres Time Level 2', '#dom-performance-now', 'performance.now()')}}</td>
<td>{{Spec2('Highres Time Level 2')}}</td>
<td>Stricter definitions of interfaces and types.</td>
</tr>
<tr>
<td>{{SpecName('Highres Time', '#dom-performance-now', 'performance.now()')}}</td>
<td>{{Spec2('Highres Time')}}</td>
<td>Initial definition</td>
</tr>
</tbody>
</table>
<h2 id="Browser_compatibility">Compatibilidade com navegadores</h2>
<p>{{CompatibilityTable}}</p>
<div id="compat-desktop">
<table class="compat-table">
<tbody>
<tr>
<th>Feature</th>
<th>Chrome</th>
<th>Edge</th>
<th>Firefox (Gecko)</th>
<th>Internet Explorer</th>
<th>Opera</th>
<th>Safari</th>
</tr>
<tr>
<td>Basic support</td>
<td>{{CompatChrome("20.0")}} {{property_prefix("webkit")}}<br>
{{CompatChrome("24.0")}} [1]</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatGeckoDesktop("15.0")}}</td>
<td>10.0</td>
<td>{{CompatOpera("15.0")}}</td>
<td>{{CompatSafari("8.0")}}</td>
</tr>
<tr>
<td>on Web workers</td>
<td>{{CompatChrome("33")}}</td>
<td>{{CompatUnknown}}</td>
<td>{{CompatGeckoDesktop("34.0")}}</td>
<td>{{CompatUnknown}}</td>
<td>{{CompatUnknown}}</td>
<td>{{CompatUnknown}}</td>
</tr>
<tr>
<td><code>now()</code> in a dedicated worker is now separate from the main context's <code>now()</code>.</td>
<td>{{CompatUnknown}}</td>
<td>{{CompatUnknown}}</td>
<td>{{CompatGeckoDesktop("45.0")}}</td>
<td>{{CompatUnknown}}</td>
<td>{{CompatUnknown}}</td>
<td>{{CompatUnknown}}</td>
</tr>
</tbody>
</table>
</div>
<div id="compat-mobile">
<table class="compat-table">
<tbody>
<tr>
<th>Feature</th>
<th>Android</th>
<th>Android Webview</th>
<th>Edge</th>
<th>Firefox Mobile (Gecko)</th>
<th>IE Mobile</th>
<th>Opera Mobile</th>
<th>Safari Mobile</th>
<th>Chrome for Android</th>
</tr>
<tr>
<td>Basic support</td>
<td>{{CompatAndroid("4.0")}}</td>
<td>{{CompatChrome("25.0")}}</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatGeckoMobile("15.0")}}</td>
<td>10.0</td>
<td>{{CompatNo}}</td>
<td>9</td>
<td>{{CompatChrome("25.0")}}</td>
</tr>
<tr>
<td>on Web workers</td>
<td>{{CompatUnknown}}</td>
<td>{{CompatVersionUnknown}}</td>
<td>{{CompatUnknown}}</td>
<td>{{CompatGeckoMobile("34.0")}}</td>
<td>{{CompatUnknown}}</td>
<td>{{CompatUnknown}}</td>
<td>{{CompatUnknown}}</td>
<td>{{CompatVersionUnknown}}</td>
</tr>
<tr>
<td><code>now()</code> in a dedicated worker is now separate from the main context's <code>now()</code>.</td>
<td>{{CompatUnknown}}</td>
<td>{{CompatUnknown}}</td>
<td>{{CompatUnknown}}</td>
<td>{{CompatGeckoMobile("45.0")}}</td>
<td>{{CompatUnknown}}</td>
<td>{{CompatUnknown}}</td>
<td>{{CompatUnknown}}</td>
<td>{{CompatUnknown}}</td>
</tr>
</tbody>
</table>
</div>
<p>[1] Windows versions of Chrome 20 through 33 return <code>performance.now()</code> only to millisecond precision.</p>
<h2 id="Veja_também">Veja também</h2>
<ul>
<li><a href="http://updates.html5rocks.com/2012/08/When-milliseconds-are-not-enough-performance-now">When milliseconds are not enough: performance.now() </a>from HTML5 Rocks.</li>
</ul>
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