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+---
+title: PerformanceTiming.unloadEventStart
+slug: Web/API/PerformanceTiming/unloadEventStart
+translation_of: Web/API/PerformanceTiming/unloadEventStart
+---
+<p>{{APIRef("Navigation Timing")}}</p>
+
+<h2 id="概要">概要</h2>
+
+<p><code><strong>PerformanceTiming</strong></code><strong><code>.unloadEventStart</code></strong> 是一个返回代表一个时刻的 <code>unsigned long long</code> 型只读属性，为 {{event("unload")}} 事件被触发之时的 Unix毫秒时间戳。如果没有上一个文档，或者上一个文档或需要重定向的页面之一不同源，则该值返回 <code>0。</code></p>
+
+<h2 id="语法">语法</h2>
+
+<pre class="syntaxbox"><em>time</em> = <em>performanceTiming</em>.unloadEventStart;</pre>
+
+<h2 id="标准">标准</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('Navigation Timing', '#dom-performancetiming-unloadeventstart', 'PerformanceTiming.unloadEventStart')}}</td>
+   <td>{{Spec2('Navigation Timing')}}</td>
+   <td>Initial definition.</td>
+  </tr>
+ </tbody>
+</table>
+
+<h2 id="浏览器兼容性">浏览器兼容性</h2>
+
+<div>
+<div>
+
+
+<p>{{Compat("api.PerformanceTiming.unloadEventStart")}}</p>
+</div>
+</div>
+
+<h2 id="参见">参见</h2>
+
+<ul>
+ <li>它属于 {{domxref("PerformanceTiming")}} 接口。</li>
+</ul>