From 33058f2b292b3a581333bdfb21b8f671898c5060 Mon Sep 17 00:00:00 2001
From: Peter Bengtsson <mail@peterbe.com>
Date: Tue, 8 Dec 2020 14:40:17 -0500
Subject: initial commit

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+---
+title: yield*
+slug: Web/JavaScript/Reference/Operators/yield*
+tags:
+  - ECMAScript 2015
+  - Generators
+  - Iterable
+  - Iterator
+  - JavaScript
+  - Operator
+  - Reference
+translation_of: Web/JavaScript/Reference/Operators/yield*
+---
+<div>{{jsSidebar("Operators")}}</div>
+
+<p> <strong><code>yield*</code> 表达式</strong>用于委托给另一个{{jsxref("Statements/function*", "generator")}} 或可迭代对象。</p>
+
+<h2 id="Syntax" name="Syntax">语法</h2>
+
+<pre class="syntaxbox"> yield* [[expression]];</pre>
+
+<dl>
+ <dt><code>expression</code></dt>
+ <dd>返回一个可迭代对象的表达式。</dd>
+</dl>
+
+<h2 id="描述">描述</h2>
+
+<p><code>yield*</code> 表达式迭代操作数，并产生它返回的每个值。</p>
+
+<p><code>yield*</code> 表达式本身的值是当迭代器关闭时返回的值（即<code>done</code>为<code>true</code>时）。</p>
+
+<h2 id="Examples" name="Examples">示例</h2>
+
+<h3 id="委托给其他生成器">委托给其他生成器</h3>
+
+<p>以下代码中，<code>g1()</code> <code>yield</code> 出去的每个值都会在 <code>g2()</code> 的 <code>next()</code> 方法中返回，就像那些 <code>yield</code> 语句是写在 <code>g2()</code> 里一样。</p>
+
+<pre class="brush: js">function* g1() {
+  yield 2;
+  yield 3;
+  yield 4;
+}
+
+function* g2() {
+  yield 1;
+  yield* g1();
+  yield 5;
+}
+
+var iterator = g2();
+
+console.log(iterator.next()); // { value: 1, done: false }
+console.log(iterator.next()); // { value: 2, done: false }
+console.log(iterator.next()); // { value: 3, done: false }
+console.log(iterator.next()); // { value: 4, done: false }
+console.log(iterator.next()); // { value: 5, done: false }
+console.log(iterator.next()); // { value: undefined, done: true }
+</pre>
+
+<h3 id="委托给其他可迭代对象">委托给其他可迭代对象</h3>
+
+<p>除了生成器对象这一种可迭代对象，<code>yield*</code> 还可以 <code>yield</code> 其它任意的可迭代对象，比如说数组、字符串、<code>arguments</code> 对象等等。</p>
+
+<pre class="brush: js">function* g3() {
+  yield* [1, 2];
+  yield* "34";
+  yield* arguments;
+}
+
+var iterator = g3(5, 6);
+
+console.log(iterator.next()); // { value: 1, done: false }
+console.log(iterator.next()); // { value: 2, done: false }
+console.log(iterator.next()); // { value: "3", done: false }
+console.log(iterator.next()); // { value: "4", done: false }
+console.log(iterator.next()); // { value: 5, done: false }
+console.log(iterator.next()); // { value: 6, done: false }
+console.log(iterator.next()); // { value: undefined, done: true }
+</pre>
+
+<h3 id="yield*_表达式的值"><code>yield*</code> 表达式的值</h3>
+
+<p><code>yield*</code> 是一个表达式，不是语句，所以它会有自己的值。</p>
+
+<pre class="brush: js">function* g4() {
+  yield* [1, 2, 3];
+  return "foo";
+}
+
+var result;
+
+function* g5() {
+  result = yield* g4();
+}
+
+var iterator = g5();
+
+console.log(iterator.next()); // { value: 1, done: false }
+console.log(iterator.next()); // { value: 2, done: false }
+console.log(iterator.next()); // { value: 3, done: false }
+console.log(iterator.next()); // { value: undefined, done: true },
+                              // 此时 g4() 返回了 { value: "foo", done: true }
+
+console.log(result);          // "foo"
+</pre>
+
+<h2 id="Specifications" name="Specifications">规范</h2>
+
+<table class="standard-table">
+ <thead>
+  <tr>
+   <th scope="col">Specification</th>
+   <th scope="col">Status</th>
+   <th scope="col">Comment</th>
+  </tr>
+ </thead>
+ <tbody>
+  <tr>
+   <td>{{SpecName('ES2015', '#', 'Yield')}}</td>
+   <td>{{Spec2('ES2015')}}</td>
+   <td>Initial definition.</td>
+  </tr>
+  <tr>
+   <td>{{SpecName('ESDraft', '#', 'Yield')}}</td>
+   <td>{{Spec2('ESDraft')}}</td>
+   <td> </td>
+  </tr>
+ </tbody>
+</table>
+
+<h2 id="Browser_compatibility" name="Browser_compatibility">浏览器兼容</h2>
+
+<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 href="https://github.com/mdn/browser-compat-data">https://github.com/mdn/browser-compat-data</a> and send us a pull request.</div>
+
+<p>{{Compat("javascript.operators.yield_star")}}</p>
+
+<h2 id="Firefox_特别提示">Firefox 特别提示</h2>
+
+<ul>
+ <li>从 Gecko 33 {{geckoRelease(33)}} 开始，<code>yield</code>表达式的解析已被更新以符合ES2015规范（{{bug(981599)}}）：
+
+  <ul>
+   <li>现在有行结束符限制。在 <code>yield</code> 和 <code>*</code> 之间不允许有换行符。如下代码会抛出{{jsxref("SyntaxError")}}：
+
+    <pre class="brush: js">function* foo() {
+  yield
+  *[];
+}</pre>
+   </li>
+  </ul>
+ </li>
+</ul>
+
+<h2 id="See_also" name="See_also">相关链接</h2>
+
+<ul>
+ <li><a href="/zh-CN/docs/Web/JavaScript/Guide/The_Iterator_protocol">迭代器协议</a></li>
+ <li>{{jsxref("Statements/function*", "function*")}}</li>
+ <li>{{jsxref("Operators/function*", "function* expression")}}</li>
+ <li>{{jsxref("Operators/yield", "yield")}}</li>
+</ul>
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