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158 lines
11 KiB
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<article id="wikiArticle">
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<div></div>
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<p><strong><code>Promise.race(iterable)</code> </strong>方法返回一个 promise,一旦迭代器中的某个promise解决或拒绝,返回的 promise就会解决或拒绝。</p>
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<div><iframe class="interactive interactive-js" frameborder="0" height="250" src="https://interactive-examples.mdn.mozilla.net/pages/js/promise-race.html" width="100%"></iframe></div>
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<p class="hidden">The source for this interactive demo is stored in a GitHub repository. If you'd like to contribute to the interactive demo project, please clone <a class="external" href="https://github.com/mdn/interactive-examples" rel="noopener">https://github.com/mdn/interactive-examples</a> and send us a pull request.</p>
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<h2 id="Syntax" name="Syntax">语法</h2>
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<pre><code class="language-javascript"><var>Promise.race(iterable)</var>;</code></pre>
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<h3 id="参数"><strong>参数</strong></h3>
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<dl>
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<dt>iterable</dt>
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<dd>可迭代对象,类似<a href="Reference/Array" title="REDIRECT Array"><code>Array</code></a>。详见 <a href="/en-US/docs/Web/JavaScript/Guide/iterable">iterable</a>。</dd>
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</dl>
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<h3 id="返回值">返回值</h3>
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<p>一个<strong>待定的</strong> <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> 只要给定的迭代中的一个promise解决或拒绝,就采用第一个promise的值作为它的值,从而<strong>异步</strong>地解析或拒绝(一旦堆栈为空)。</p>
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<h2 id="Description" name="Description">描述</h2>
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<p><code>race</code> 函数返回一个 <code>Promise</code>,它将与第一个传递的 promise 相同的完成方式被完成。它可以是完成( resolves),也可以是失败(rejects),这要取决于第一个完成的方式是两个中的哪个。</p>
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<p>如果传的迭代是空的,则返回的 promise 将永远等待。</p>
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<p>如果迭代包含一个或多个非承诺值和/或已解决/拒绝的承诺,则<code> Promise.race</code> 将解析为迭代中找到的第一个值。</p>
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<h2 id="示例">示例</h2>
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<h3 id="Promise.race的异步性"><code>Promise.race</code>的异步性</h3>
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<pre><code>// we are passing as argument an array of promises that are already resolved,
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// to trigger Promise.race as soon as possible
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var resolvedPromisesArray = [Promise.resolve(33), Promise.resolve(44)];
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var p = Promise.race(resolvedPromisesArray);
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// immediately logging the value of p
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console.log(p);
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// using setTimeout we can execute code after the stack is empty
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setTimeout(function(){
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console.log('the stack is now empty');
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console.log(p);
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});
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// logs, in order:
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// Promise { <state>: "pending" }
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// the stack is now empty
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// Promise { <state>: "fulfilled", <value>: 33 }</code></code></pre>
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<h3 id="使用_Promise.race_–_setTimeout_的示例"><code><font face="Open Sans, sans-serif">使用 </font>Promise.race</code> – <code>setTimeout 的示例</code></h3>
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<pre><code class="language-javascript">var p1 = new Promise(function(resolve, reject) {
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setTimeout(resolve, 500, "one");
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});
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var p2 = new Promise(function(resolve, reject) {
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setTimeout(resolve, 100, "two");
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});
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Promise.race([p1, p2]).then(function(value) {
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console.log(value); // "two"
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// 两个都完成,但 p2 更快
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});
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var p3 = new Promise(function(resolve, reject) {
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setTimeout(resolve, 100, "three");
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});
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var p4 = new Promise(function(resolve, reject) {
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setTimeout(reject, 500, "four");
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});
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Promise.race([p3, p4]).then(function(value) {
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console.log(value); // "three"
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// p3 更快,所以它完成了
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}, function(reason) {
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// 未被调用
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});
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var p5 = new Promise(function(resolve, reject) {
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setTimeout(resolve, 500, "five");
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});
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var p6 = new Promise(function(resolve, reject) {
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setTimeout(reject, 100, "six");
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});
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Promise.race([p5, p6]).then(function(value) {
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// 未被调用
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}, function(reason) {
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console.log(reason); // "six"
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// p6 更快,所以它失败了
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});
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</code></pre>
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<h2 id="规范">规范</h2>
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<table class="standard-table">
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<tbody>
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<tr>
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<th scope="col">Specification</th>
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<th scope="col">Status</th>
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<th scope="col">Comment</th>
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</tr>
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<tr>
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<td><a class="external" href="https://www.ecma-international.org/ecma-262/6.0/#sec-promise.race" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">Promise.race</small></a></td>
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<td><span class="spec-Standard">Standard</span></td>
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<td>Initial definition in an ECMA standard.</td>
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</tr>
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<tr>
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<td><a class="external" href="https://tc39.github.io/ecma262/#sec-promise.race" hreflang="en" lang="en" rel="noopener">ECMAScript Latest Draft (ECMA-262)<br/><small lang="zh-CN">Promise.race</small></a></td>
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<td><span class="spec-Draft">Draft</span></td>
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<td> </td>
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</tr>
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</tbody>
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</table>
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<h2 id="浏览器兼容">浏览器兼容</h2>
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<p class="hidden">The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out <a class="external" href="https://github.com/mdn/browser-compat-data" rel="noopener">https://github.com/mdn/browser-compat-data</a> and send us a pull request.</p>
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<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>race</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">
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<span>Full support</span>
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</abbr>
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32</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">
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<span>Full support</span>
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</abbr>
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12</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">
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<span>Full support</span>
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</abbr>
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29</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">
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<span>No support</span>
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</abbr>
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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">
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<span>Full support</span>
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</abbr>
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19</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">
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<span>Full support</span>
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</abbr>
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8</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">
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<span>Full support</span>
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</abbr>
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4.4.3</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">
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<span>Full support</span>
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</abbr>
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32</td><td class="bc-supports-yes bc-browser-edge_mobile"><span class="bc-browser-name">Edge Mobile</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</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">
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<span>Full support</span>
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</abbr>
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29</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">
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<span>Full support</span>
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</abbr>
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Yes</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">
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<span>Full support</span>
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</abbr>
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8</td><td class="bc-supports-yes bc-browser-samsunginternet_android"><span class="bc-browser-name">Samsung Internet Android</span><abbr class="bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr>
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Yes</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">
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<span>Full support</span>
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</abbr>
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0.12</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">
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<abbr class="bc-level bc-level-yes only-icon" title="Full support">
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<span>Full support</span>
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</abbr></span></dt><dd>Full support</dd><dt><span class="bc-supports-no bc-supports">
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<abbr class="bc-level bc-level-no only-icon" title="No support">
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<span>No support</span>
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</abbr></span></dt><dd>No support</dd></dl></section></div><p></p>
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<h2 id="相关链接">相关链接</h2>
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<ul>
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<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>
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<li><a href="Reference/Global_Objects/Promise/all" title="Promise.all(iterable) 方法返回一个 Promise 实例,此实例在 iterable 参数内所有的 promise 都“完成(resolved)”或参数中不包含 promise 时回调完成(resolve);如果参数中 promise 有一个失败(rejected),此实例回调失败(reject),失败原因的是第一个失败 promise 的结果。"><code>Promise.all()</code></a></li>
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</ul>
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</article> |