uTools-Manuals/docs/javascript/Reference/Global_Objects/Promise/finally.html

<article id="wikiArticle">
<div></div>
<div> </div>
<div><code><strong>finally()</strong></code> 方法返回一个<a href="Reference/Global_Objects/Promise" title="Promise 对象用于表示一个异步操作的最终状态（完成或失败），以及该异步操作的结果值。"><code>Promise</code></a>，在promise执行结束时，无论结果是fulfilled或者是rejected，在执行<a href="Reference/Global_Objects/Promise/then" title="then() 方法返回一个  Promise 。它最多需要有两个参数：Promise 的成功和失败情况的回调函数。"><code>then()</code></a>和<a href="Reference/Global_Objects/Promise/catch" title="catch() 方法返回一个Promise，并且处理拒绝的情况。它的行为与调用Promise.prototype.then(undefined, onRejected) 相同。 (事实上, calling obj.catch(onRejected) 内部calls obj.then(undefined, onRejected))."><code>catch()</code></a>后，都会执行<strong><code>finally</code></strong>指定的回调函数。这为指定执行完promise后，无论结果是fulfilled还是rejected都需要执行的代码提供了一种方式，避免同样的语句需要在<a href="Reference/Global_Objects/Promise/then" title="then() 方法返回一个  Promise 。它最多需要有两个参数：Promise 的成功和失败情况的回调函数。"><code>then()</code></a>和<a href="Reference/Global_Objects/Promise/catch" title="catch() 方法返回一个Promise，并且处理拒绝的情况。它的行为与调用Promise.prototype.then(undefined, onRejected) 相同。 (事实上, calling obj.catch(onRejected) 内部calls obj.then(undefined, onRejected))."><code>catch()</code></a>中各写一次的情况。</div>
<h2 id="语法">语法</h2>
<pre><code class="language-javascript"><var>p.finally(onFinally)</var>;

p.finally(function() {
   // 返回状态为(resolved 或 rejected)
});参数</code></pre>
<dl>
<dt><code>onFinally</code></dt>
<dd><code>Promise</code> 状态改变后执行的回调函数。</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<a href="Reference/Global_Objects/Promise" title="Promise 对象用于表示一个异步操作的最终状态（完成或失败），以及该异步操作的结果值。"><code>Promise</code></a>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><code  class="language-javascript">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; });

</code></pre>
<h2 id="规范">规范</h2>
<table class="standard-table">
<tbody>
<tr>
<th scope="col">规范</th>
<th scope="col">状态</th>
<th scope="col">备注</th>
</tr>
<tr>
<td><a class="external" href="https://github.com/tc39/proposal-promise-finally" rel="noopener">TC39 proposal</a></td>
<td>Stage 4</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 class="external" href="https://github.com/mdn/browser-compat-data" rel="noopener">https://github.com/mdn/browser-compat-data</a>.</p>
<p></p><div class="bc-data"><a class="bc-github-link external" href="https://github.com/mdn/browser-compat-data" rel="noopener">Update compatibility data on GitHub</a><table class="bc-table bc-table-js"><thead><tr class="bc-platforms"><td></td><th class="bc-platform-desktop" colspan="6"><span>Desktop</span></th><th class="bc-platform-mobile" colspan="7"><span>Mobile</span></th><th class="bc-platform-server" colspan="1"><span>Server</span></th></tr><tr class="bc-browsers"><td></td><th class="bc-browser-chrome"><span class="bc-head-txt-label bc-head-icon-chrome">Chrome</span></th><th class="bc-browser-edge"><span class="bc-head-txt-label bc-head-icon-edge">Edge</span></th><th class="bc-browser-firefox"><span class="bc-head-txt-label bc-head-icon-firefox">Firefox</span></th><th class="bc-browser-ie"><span class="bc-head-txt-label bc-head-icon-ie">Internet Explorer</span></th><th class="bc-browser-opera"><span class="bc-head-txt-label bc-head-icon-opera">Opera</span></th><th class="bc-browser-safari"><span class="bc-head-txt-label bc-head-icon-safari">Safari</span></th><th class="bc-browser-webview_android"><span class="bc-head-txt-label bc-head-icon-webview_android">Android webview</span></th><th class="bc-browser-chrome_android"><span class="bc-head-txt-label bc-head-icon-chrome_android">Chrome for Android</span></th><th class="bc-browser-edge_mobile"><span class="bc-head-txt-label bc-head-icon-edge_mobile">Edge Mobile</span></th><th class="bc-browser-firefox_android"><span class="bc-head-txt-label bc-head-icon-firefox_android">Firefox for Android</span></th><th class="bc-browser-opera_android"><span class="bc-head-txt-label bc-head-icon-opera_android">Opera for Android</span></th><th class="bc-browser-safari_ios"><span class="bc-head-txt-label bc-head-icon-safari_ios">Safari on iOS</span></th><th class="bc-browser-samsunginternet_android"><span class="bc-head-txt-label bc-head-icon-samsunginternet_android">Samsung Internet</span></th><th class="bc-browser-nodejs"><span class="bc-head-txt-label bc-head-icon-nodejs">Node.js</span></th></tr></thead><tbody><tr><th scope="row"><code>finally</code></th><td class="bc-supports-yes bc-browser-chrome"><span class="bc-browser-name">Chrome</span><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
              63</td><td class="bc-supports-yes bc-browser-edge"><span class="bc-browser-name">Edge</span><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
              18</td><td class="bc-supports-yes bc-browser-firefox"><span class="bc-browser-name">Firefox</span><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
              58</td><td class="bc-supports-no bc-browser-ie"><span class="bc-browser-name">IE</span><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>
              No</td><td class="bc-supports-yes bc-browser-opera"><span class="bc-browser-name">Opera</span><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
              50</td><td class="bc-supports-yes bc-browser-safari"><span class="bc-browser-name">Safari</span><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
              11.1</td><td class="bc-supports-yes bc-browser-webview_android"><span class="bc-browser-name">WebView Android</span><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
              63</td><td class="bc-supports-yes bc-browser-chrome_android"><span class="bc-browser-name">Chrome Android</span><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
              63</td><td class="bc-supports-no bc-browser-edge_mobile"><span class="bc-browser-name">Edge Mobile</span><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>
              No</td><td class="bc-supports-yes bc-browser-firefox_android"><span class="bc-browser-name">Firefox Android</span><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
              58</td><td class="bc-supports-yes bc-browser-opera_android"><span class="bc-browser-name">Opera Android</span><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
              50</td><td class="bc-supports-yes bc-browser-safari_ios"><span class="bc-browser-name">Safari iOS</span><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
              11.1</td><td class="bc-supports-no bc-browser-samsunginternet_android"><span class="bc-browser-name">Samsung Internet Android</span><abbr class="bc-level-no only-icon" title="No support">
<span>No support</span>
</abbr>
              No</td><td class="bc-supports-yes bc-browser-nodejs"><span class="bc-browser-name">nodejs</span><abbr class="bc-level-yes only-icon" title="Full support">
<span>Full support</span>
</abbr>
              10.0.0</td></tr></tbody></table><section class="bc-legend" id="sect1"><h3 class="offscreen" id="Legend">Legend</h3><dl><dt><span class="bc-supports-yes bc-supports">
<abbr class="bc-level bc-level-yes only-icon" title="Full support">
<span>Full support</span>
                  
                </abbr></span></dt><dd>Full support</dd><dt><span class="bc-supports-no bc-supports">
<abbr class="bc-level bc-level-no only-icon" title="No support">
<span>No support</span>
                  
                </abbr></span></dt><dd>No support</dd></dl></section></div><p></p>
<h2 id="参见">参见</h2>
<ul>
<li><a href="Reference/Global_Objects/Promise" title="Promise 对象用于表示一个异步操作的最终状态（完成或失败），以及该异步操作的结果值。"><code>Promise</code></a></li>
<li><a href="Reference/Global_Objects/Promise/then" title="then() 方法返回一个  Promise 。它最多需要有两个参数：Promise 的成功和失败情况的回调函数。"><code>Promise.prototype.then()</code></a></li>
<li><a href="Reference/Global_Objects/Promise/catch" title="catch() 方法返回一个Promise，并且处理拒绝的情况。它的行为与调用Promise.prototype.then(undefined, onRejected) 相同。 (事实上, calling obj.catch(onRejected) 内部calls obj.then(undefined, onRejected))."><code>Promise.prototype.catch()</code></a></li>
</ul>
</article>