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+---
+title: ExtendableEvent
+slug: Web/API/ExtendableEvent
+tags:
+  - API
+  - Experimental
+  - ExtendableEvent
+  - Interface
+  - NeedsTranslation
+  - Offline
+  - Reference
+  - Service Workers
+  - ServiceWorker
+  - TopicStub
+  - Workers
+translation_of: Web/API/ExtendableEvent
+---
+<div>{{APIRef("Service Workers API")}}{{SeeCompatTable}}</div>
+
+<div>作为 service worker 生命周期的一部分，<strong><code>ExtendableEvent</code></strong>接口延长了在全局范围上{{event("install")}}和{{event("activate")}}事件的生命周期。这样可以确保在升级数据库架构并删除过时的caches之前，不会调度任何函数事件（如{{domxref("FetchEvent")}}）。</div>
+
+<div>如果在<code>ExtendableEvent</code>处理程序之外调用{{domxref("ExtendableEvent.waitUntil","waitUntil()")}}，浏览器应该抛出一个<code>InvalidStateError</code>；还要注意，多个调用将堆积起来，结果promises 将添加到<a href="https://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#dfn-extend-lifetime-promises">extend lifetime promises</a>.</div>
+
+<div> </div>
+
+<div class="note">
+<p><strong>提示</strong>: 上述段落中描述的行为在firefox 43中得到了修复（参见 {{bug(1180274)}} ）。</p>
+</div>
+
+<p>此接口继承自{{domxref("Event")}}接口。</p>
+
+<p>{{InheritanceDiagram(700, 60, 20)}}</p>
+
+<div class="note">
+<p><strong>提示</strong>: 只有当全局范围是 {{domxref("ServiceWorkerGlobalScope")}} 时，此接口才可用。当它是一个 {{domxref("Window")}} 或其他类型 worker 的作用域时，它不可用。</p>
+</div>
+
+<h2 id="构造函数">构造函数</h2>
+
+<dl>
+ <dt>{{domxref("ExtendableEvent.ExtendableEvent()", "ExtendableEvent()")}}</dt>
+ <dd>创建新的<code>ExtendableEvent</code>对象。</dd>
+</dl>
+
+<h2 id="特性">特性</h2>
+
+<p>不实现任何特定属性，但从其父级事件继承属，<em>{{domxref("Event")}}</em>。</p>
+
+<h2 id="方法">方法</h2>
+
+<p><em>从他的父辈继承, </em><em>{{domxref("Event")}}</em>.</p>
+
+<dl>
+ <dt>{{domxref("ExtendableEvent.waitUntil", "ExtendableEvent.waitUntil()")}}</dt>
+ <dd>
+ <p>延长事件的生存期。它将在service worker 的 <code><a href="https://developer.mozilla.org/en-US/docs/Web/API/ServiceWorkerGlobalScope/install">install</a></code> 和 <code><a href="https://developer.mozilla.org/en-US/docs/Web/API/ServiceWorkerGlobalScope/activate">activate</a></code> 事件中被调用。</p>
+ </dd>
+</dl>
+
+<h2 id="实例">实例</h2>
+
+<p>代码片段来自<a href="https://github.com/GoogleChrome/samples/blob/gh-pages/service-worker/prefetch/service-worker.js">service worker prefetch sample</a> (查看 <a href="https://googlechrome.github.io/samples/service-worker/prefetch/">prefetch example live</a>.)。代码在{{domxref("ServiceWorkerGlobalScope.oninstall")}}中调用{{domxref("ExtendableEvent.waitUntil()")}}，延迟将{{domxref("ServiceWorkerRegistration.installing")}} Worker视为已安装，直到传递的promise resolve(在所有资源都已被提取和缓存的情况，或者发生任何异常时的问题.)</p>
+
+<p>代码段还显示了对service worker使用的缓存进行版本控制的最佳实践。虽然在这个例子中只有一个缓存，但是相同的方法可以用于多个缓存。它将缓存的速记标识符映射到特定的、版本化的缓存名称。</p>
+
+<div class="note">
+<p><strong>提示</strong>:在chrome中，日志记录语句通过chrome://service worker internals访问的相关服务工作者的“inspect”接口可见。</p>
+</div>
+
+<pre class="brush: js">var CACHE_VERSION = 1;
+var CURRENT_CACHES = {
+  prefetch: 'prefetch-cache-v' + CACHE_VERSION
+};
+
+self.addEventListener('install', function(event) {
+  var urlsToPrefetch = [
+    './static/pre_fetched.txt',
+    './static/pre_fetched.html',
+    'https://www.chromium.org/_/rsrc/1302286216006/config/customLogo.gif'
+  ];
+
+  console.log('Handling install event. Resources to pre-fetch:', urlsToPrefetch);
+
+  event.waitUntil(
+    caches.open(CURRENT_CACHES['prefetch']).then(function(cache) {
+      cache.addAll(urlsToPrefetch.map(function(urlToPrefetch) {
+        return new Request(urlToPrefetch, {mode: 'no-cors'});
+      })).then(function() {
+        console.log('All resources have been fetched and cached.');
+      });
+    }).catch(function(error) {
+      console.error('Pre-fetching failed:', error);
+    })
+  );
+});</pre>
+
+<div class="note"><strong>重点</strong>: 在获取资源时，如果有可能资源是由不支持 <a href="http://en.wikipedia.org/wiki/Cross-origin_resource_sharing">CORS</a> 的服务器提供的，那么使用 <code>{mode: 'no-cors'}</code> 非常重要。在本例中， <a href="http://www.chromium.org">www.chromium.org</a> 不支持CORS。</div>
+
+<h2 id="Specifications">Specifications</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('Service Workers', '#extendable-event', 'ExtendableEvent')}}</td>
+   <td>{{Spec2('Service Workers')}}</td>
+   <td>Initial definition.</td>
+  </tr>
+ </tbody>
+</table>
+
+<h2 id="Browser_compatibility">Browser compatibility</h2>
+
+<div>{{CompatibilityTable}}</div>
+
+<div id="compat-desktop">
+<table class="compat-table">
+ <tbody>
+  <tr>
+   <th>Feature</th>
+   <th>Chrome</th>
+   <th>Firefox (Gecko)</th>
+   <th>Internet Explorer</th>
+   <th>Opera</th>
+   <th>Safari (WebKit)</th>
+  </tr>
+  <tr>
+   <td>Basic support</td>
+   <td>{{CompatChrome(40.0)}}</td>
+   <td>{{ CompatGeckoDesktop("44.0") }}<sup>[1]</sup></td>
+   <td>{{CompatNo}}</td>
+   <td>24</td>
+   <td>{{CompatNo}}</td>
+  </tr>
+  <tr>
+   <td>async <code>waitUntil()</code></td>
+   <td>{{CompatUnknown}}</td>
+   <td>{{ CompatGeckoDesktop("53.0") }}<sup>[2]</sup></td>
+   <td>{{CompatNo}}</td>
+   <td>{{CompatUnknown}}</td>
+   <td>{{CompatNo}}</td>
+  </tr>
+ </tbody>
+</table>
+</div>
+
+<div id="compat-mobile">
+<table class="compat-table">
+ <tbody>
+  <tr>
+   <th>Feature</th>
+   <th>Android</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>{{CompatNo}}</td>
+   <td>{{ CompatGeckoMobile("44.0") }}</td>
+   <td>{{CompatNo}}</td>
+   <td>{{CompatUnknown}}</td>
+   <td>{{CompatNo}}</td>
+   <td>{{CompatChrome(40.0)}}</td>
+  </tr>
+  <tr>
+   <td>async <code>waitUntil()</code></td>
+   <td>{{CompatNo}}</td>
+   <td>{{ CompatGeckoMobile("53.0") }}<sup>[2]</sup></td>
+   <td>{{CompatNo}}</td>
+   <td>{{CompatUnknown}}</td>
+   <td>{{CompatNo}}</td>
+   <td>{{CompatUnknown}}</td>
+  </tr>
+ </tbody>
+</table>
+</div>
+
+<p>[1] Service workers (and <a href="/en-US/docs/Web/API/Push_API">Push</a>) have been disabled in the <a href="https://www.mozilla.org/en-US/firefox/organizations/">Firefox 45 &amp; 52 Extended Support Releases</a> (ESR.)</p>
+
+<p>[2] {{domxref("ExtendableEvent.waitUntil", "ExtendableEvent.waitUntil()")}} can now be called asynchronously (see {{bug(1263304)}}).</p>
+
+<h2 id="See_also">See also</h2>
+
+<ul>
+ <li><a href="https://developer.mozilla.org/en-US/docs/Web/API/ServiceWorker_API/Using_Service_Workers">Using Service Workers</a></li>
+ <li><a class="external external-icon" href="https://github.com/mdn/sw-test">Service workers basic code example</a></li>
+ <li><a class="external external-icon" href="https://jakearchibald.github.io/isserviceworkerready/">Is ServiceWorker ready?</a></li>
+ <li>{{jsxref("Promise")}}</li>
+ <li><a href="https://developer.mozilla.org/en-US/docs/Web/Guide/Performance/Using_web_workers">Using web workers</a></li>
+</ul>