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132 lines
11 KiB
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<article id="wikiArticle">
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<div></div>
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<p>The <strong><code>for await...of</code> 语句</strong>在异步或者同步可迭代对象上（包括 <a href="Reference/String" title="此页面仍未被本地化, 期待您的翻译!"><code>String</code></a>，<a href="Reference/Array" title="REDIRECT Array"><code>Array</code></a>，<code>Array</code>-like 对象（比如<a href="Reference/Functions/arguments" title="arguments 是一个对应于传递给函数的参数的类数组对象。"><code>arguments</code></a> 或者<a href="/zh-CN/docs/Web/API/NodeList" title="NodeList 对象是一个节点的集合，是由 Node.childNodes 和 document.querySelectorAll 返回的."><code>NodeList</code></a>)，<a href="Reference/Global_Objects/TypedArray" title="一个TypedArray 对象描述一个底层的二进制数据缓存区的一个类似数组(array-like)视图。事实上，没有名为 TypedArray的全局对象，也没有一个名为的 TypedArray构造函数。相反，有许多不同的全局对象，下面会列出这些针对特定元素类型的类型化数组的构造函数。在下面的页面中，你会找到一些不管什么类型都公用的属性和方法。"><code>TypedArray</code></a>，<a href="Reference/Map" title="此页面仍未被本地化, 期待您的翻译!"><code>Map</code></a>， <a href="Reference/Global_Objects/Set" title="Set 对象允许你存储任何类型的唯一值，无论是原始值或者是对象引用。"><code>Set</code></a>和其他对象等等）创建一个迭代循环，调用自定义迭代钩子，并为每个不同属性的值执行语句<strong>。</strong></p>
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<p class="hidden">The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples 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="语法">语法</h2>
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<pre><code class="language-javascript">for await (<em>variable</em> of <em>iterable</em>) {
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<em>statement
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</em>}
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</code></pre>
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<dl>
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<dt><code>variable</code></dt>
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<dd>在每次迭代中，将不同属性的值分配给变量。</dd>
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<dt><code>iterable</code></dt>
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<dd>被迭代枚举其属性的对象。</dd>
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</dl>
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<h3 id="迭代异步可迭代对象">迭代异步可迭代对象</h3>
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<p>你还可以迭代一个明确实现异步迭代协议的对象：</p>
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<pre><code class="language-js">var asyncIterable = {
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[Symbol.asyncIterator]() {
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return {
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i: 0,
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next() {
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if (this.i < 3) {
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return Promise.resolve({ value: this.i++, done: false });
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}
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return Promise.resolve({ done: true });
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}
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};
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}
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};
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(async function() {
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for await (num of asyncIterable) {
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console.log(num);
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}
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})();
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// 0
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// 1
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// 2
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</code></pre>
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<h3 id="迭代异步生成器">迭代异步生成器 </h3>
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<p>异步生成器已经实现了异步迭代器协议, 所以可以用 <code>for await...of</code>循环。</p>
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<pre>async function* asyncGenerator() {
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var i = 0;
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while (i < 3) {
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yield i++;
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}
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}
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(async function() {
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for await (num of asyncGenerator()) {
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console.log(num);
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}
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})();
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// 0
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// 1
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// 2</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://tc39.github.io/ecma262/#sec-for-in-and-for-of-statements" hreflang="en" lang="en" rel="noopener">ECMAScript Latest Draft (ECMA-262)<br/><small lang="zh-CN">ECMAScript Language: The for-in, for-of, and for-await-of Statements</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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<div class="hidden">The compatibility table on 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.</div>
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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>for await...of</code> <div class="bc-icons"><abbr class="only-icon" title="Experimental. Expect behavior to change in the future."><span>Experimental</span><i class="ic-experimental"></i></abbr></div></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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63</td><td class="bc-supports-no bc-browser-edge"><span class="bc-browser-name">Edge</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-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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57</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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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">
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<span>Full support</span>
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</abbr>
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11</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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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">
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<span>Full support</span>
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</abbr>
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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">
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<span>No support</span>
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</abbr>
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No</td><td class="bc-supports-unknown bc-browser-firefox_android"><span class="bc-browser-name">Firefox Android</span><abbr title="Compatibility unknown; please update this.">
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?
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</abbr></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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50</td><td class="bc-supports-unknown bc-browser-safari_ios"><span class="bc-browser-name">Safari iOS</span><abbr title="Compatibility unknown; please update this.">
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?
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</abbr></td><td class="bc-supports-unknown bc-browser-samsunginternet_android"><span class="bc-browser-name">Samsung Internet Android</span><abbr title="Compatibility unknown; please update this.">
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?
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</abbr></td><td class="bc-supports-unknown bc-browser-nodejs"><span class="bc-browser-name">nodejs</span><abbr title="Compatibility unknown; please update this.">
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?
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</abbr></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><dt><span class="bc-supports-unknown bc-supports">
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<abbr class="bc-level bc-level-unknown only-icon" title="Compatibility unknown">
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<span>Compatibility unknown</span>
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</abbr></span></dt><dd>Compatibility unknown</dd><dt><abbr class="only-icon" title="Experimental. Expect behavior to change in the future."><span>Experimental. Expect behavior to change in the future.</span><i class="ic-experimental"></i></abbr></dt><dd>Experimental. Expect behavior to change in the future.</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/Statements/for...of" title="for...of语句在可迭代对象（包括 Array，Map，Set，String，TypedArray，arguments 对象等等）上创建一个迭代循环，调用自定义迭代钩子，并为每个不同属性的值执行语句"><code>Statements/for...of</code></a></li>
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</ul>
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</article> |