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+---
+title: Promise.prototype.finally()
+slug: Web/JavaScript/Reference/Global_Objects/Promise/finally
+tags:
+  - JavaScript
+  - Promises
+  - Reference
+  - finally
+translation_of: Web/JavaScript/Reference/Global_Objects/Promise/finally
+---
+<div>{{JSRef}}</div>
+
+<div></div>
+
+<div><code><strong>finally()</strong></code> 方法返回一个{{jsxref("Promise")}}。在promise结束时，无论结果是fulfilled或者是rejected，都会执行指定的回调函数。这为在<code>Promise</code>是否成功完成后都需要执行的代码提供了一种方式。</div>
+
+<div>这避免了同样的语句需要在{{jsxref("Promise.then", "then()")}}和{{jsxref("Promise.catch", "catch()")}}中各写一次的情况。</div>
+
+<h2 id="语法">语法</h2>
+
+<pre class="syntaxbox"><var>p.finally(onFinally)</var>;
+
+p.finally(function() {
+   // 返回状态为(resolved 或 rejected)
+});</pre>
+
+<h3 id="参数">参数</h3>
+
+<dl>
+ <dt><code>onFinally</code></dt>
+ <dd><code>Promise</code> 结束后调用的{{jsxref("Function")}}。</dd>
+</dl>
+
+<h3 id="返回值">返回值</h3>
+
+<p>返回一个设置了 <code>finally</code> 回调函数的{{jsxref("Promise")}}对象。 </p>
+
+<h2 id="描述">描述</h2>
+
+<p>如果你想在 promise 执行完毕后无论其结果怎样都做一些处理或清理时，<code>finally()</code> 方法可能是有用的。</p>
+
+<p><code>finally()</code> 虽然与 <code>.then(onFinally, onFinally)</code> 类似，它们不同的是：</p>
+
+<ul>
+ <li>调用内联函数时，不需要多次声明该函数或为该函数创建一个变量保存它。</li>
+ <li>由于无法知道<code>promise</code>的最终状态，所以<code>finally</code>的回调函数中不接收任何参数，它仅用于无论最终结果如何都要执行的情况。</li>
+ <li>与<code>Promise.resolve(2).then(() =&gt; {}, () =&gt; {})</code> （resolved的结果为<code>undefined</code>）不同，<code>Promise.resolve(2).finally(() =&gt; {})</code> resolved的结果为 <code>2</code>。</li>
+ <li>同样，<code>Promise.reject(3).then(() =&gt; {}, () =&gt; {})</code> (resolved 的结果为<code>undefined</code>), <code>Promise.reject(3).finally(() =&gt; {})</code> rejected 的结果为 <code>3</code>。</li>
+</ul>
+
+<div class="note">
+<p><strong>注意:</strong> 在<code>finally</code>回调中 <code>throw</code>（或返回被拒绝的promise）将以 <code>throw()</code> 指定的原因拒绝新的promise.</p>
+</div>
+
+<h2 id="示例">示例</h2>
+
+<pre class="brush: js">let isLoading = true;
+
+fetch(myRequest).then(function(response) {
+    var contentType = response.headers.get("content-type");
+    if(contentType &amp;&amp; contentType.includes("application/json")) {
+      return response.json();
+    }
+    throw new TypeError("Oops, we haven't got JSON!");
+  })
+  .then(function(json) { /* process your JSON further */ })
+  .catch(function(error) { console.log(error); })
+  .finally(function() { isLoading = false; });
+
+</pre>
+
+<h2 id="规范">规范</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('ESDraft', '#sec-promise.prototype.finally', 'Promise.prototype.finally')}}</td>
+   <td>{{Spec2('ESDraft')}}</td>
+   <td></td>
+  </tr>
+ </tbody>
+</table>
+
+<h2 id="浏览器兼容性">浏览器兼容性</h2>
+
+<p class="hidden">To contribute to this compatibility data, please write a pull request against this repository: <a href="https://github.com/mdn/browser-compat-data">https://github.com/mdn/browser-compat-data</a>.</p>
+
+<p>{{Compat("javascript.builtins.Promise.finally")}}</p>
+
+<h2 id="参见">参见</h2>
+
+<ul>
+ <li>{{jsxref("Promise")}}</li>
+ <li>{{jsxref("Promise.prototype.then()")}}</li>
+ <li>{{jsxref("Promise.prototype.catch()")}}</li>
+</ul>