uTools-Manuals/docs/javascript/Reference/Global_Objects/Generator/next.html

<article id="wikiArticle">
<div></div>
<p><code><strong>next</strong></code><strong><code>()</code></strong> 方法返回一个包含属性 <code>done</code> 和 <code>value</code> 的对象。该方法也可以通过接受一个参数用以向生成器传值。</p>
<h2 id="Syntax" name="Syntax">语法</h2>
<pre><code class="language-javascript"><code><var>gen</var>.next(value)</code></code></pre>
<h3 id="Parameters" name="Parameters">参数</h3>
<dl>
<dt><code>value</code></dt>
<dd>向生成器传递的值.</dd>
</dl>
<h3 id="返回值">返回值</h3>
<p>返回的<code><a href="/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object">对象</a></code>包含两个属性:</p>
<ul>
<li><code>done</code> (布尔类型)

  <ul>
<li>当迭代器遍历到迭代序列末端时返回值 <code>true</code>。此时，迭代器可以将返回值作为 <code>value</code>。</li>
<li>当迭代器仍可继续在迭代序列中向前遍历时返回值 <code>false。</code>这相当于不指定 <code>done </code>属性。</li>
</ul>
</li>
<li><code>value</code> - 迭代器返回的任意的Javascript值。当 <code>done</code> 的值为 <code>true </code>时可以忽略该值。</li>
</ul>
<h2 id="示例">示例</h2>
<h3 id="Example:_Using_test" name="Example:_Using_test">使用 <code>next()方法</code></h3>
<p>下面的例子展示了一个简单的生成器, 以及调用 <code>next</code> 后方法的返回值:</p>
<pre><code  class="language-javascript">function* gen() { 
  yield 1;
  yield 2;
  yield 3;
}

var g = gen(); // "Generator { }"
g.next();      // "Object { value: 1, done: false }"
g.next();      // "Object { value: 2, done: false }"
g.next();      // "Object { value: 3, done: false }"
g.next();      // "Object { value: undefined, done: true }"
</code></pre>
<h3 id="向生成器传值">向生成器传值</h3>
<p>在该示例中，调用 <code>next</code> 方法并传入了参数，请注意，首次调用 <code style="font-style: normal;">next</code> 方法时参数0被丢弃.</p>
<pre><code  class="language-javascript">/** gen函数运行解析：
 * i=0 时传入参数(0)，并将参数0赋给上一句yield的返回赋值，由于没有上一句yield语句，这步被忽略
 * 执行var val =100，然后执行yield val，此时g.next(i)返回{ value: 100, done: false }
 * 然后console.log(i,g.next(i).value)，打印出0 100
 *
 * i=1 时传入参数(1)，并将参数1赋给上一句yield的返回赋值,即(val = 1)
 * 然后执行console.log(val)，打印出1。
 * 接着进入第二次while循环，调用yield val，此时g.next(i)返回{ value: 1, done: false }
 * 然后console.log(i,g.next(i).value)，打印出1 1
 *
 * i=2 ....(省略)
 */
function* gen() {
   var val =100;
   while(true) {
      val = yield val;
      console.log(val);
   }
}

var g = gen();
for(let i =0;i&lt;5;i++){
   console.log(i,g.next(i).value);
}

/* 返回：
 0 100
 1
 1 1
 2
 2 2
 3
 3 3
 4
 4 4
*/</code></pre>
<p><img alt="向生成器传值的示例数据流向解析" src="https://mdn.mozillademos.org/files/15779/%E5%90%91%E7%94%9F%E6%88%90%E5%99%A8%E4%BC%A0%E5%80%BC.png"/></p>
<h2 id="Specifications" name="Specifications">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><a class="external" href="https://www.ecma-international.org/ecma-262/6.0/#sec-generator.prototype.next" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">Generator.prototype.next</small></a></td>
<td><span class="spec-Standard">Standard</span></td>
<td>初始定义</td>
</tr>
<tr>
<td><a class="external" href="https://tc39.github.io/ecma262/#sec-generator.prototype.next" hreflang="en" lang="en" rel="noopener">ECMAScript Latest Draft (ECMA-262)<br/><small lang="zh-CN">Generator.prototype.next</small></a></td>
<td><span class="spec-Draft">Draft</span></td>
<td>草案</td>
</tr>
</tbody>
</table>
<h2 id="Browser_compatibility" name="Browser_compatibility">浏览器兼容性</h2>
<div><div class="blockIndicator warning"><strong><a class="external" href="https://github.com/mdn/browser-compat-data" rel="noopener">We're converting our compatibility data into a machine-readable JSON format</a></strong>.
            This compatibility table still uses the old format,
            because we haven't yet converted the data it contains.
            <strong><a class="new" href="/zh-CN/docs/MDN/Contribute/Structures/Compatibility_tables" rel="nofollow">Find out how you can help!</a></strong></div>
<div class="htab">
<a id="AutoCompatibilityTable" name="AutoCompatibilityTable"></a>
<ul>
<li class="selected"><a>Desktop</a></li>
<li><a>Mobile</a></li>
</ul>
</div></div>
<div>
<div id="compat-desktop">
<table class="compat-table">
<tbody>
<tr>
<th>Feature</th>
<th>Chrome</th>
<th>Edge</th>
<th>Firefox (Gecko)</th>
<th>Internet Explorer</th>
<th>Opera</th>
<th>Safari</th>
</tr>
<tr>
<td>Basic support</td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td>13</td>
<td><a href="/en-US/Firefox/Releases/26" title="Released on 2013-12-10.">26</a> (26)</td>
<td><span style="color: #f00;">未实现</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td>10</td>
</tr>
</tbody>
</table>
</div>
<div id="compat-mobile">
<table class="compat-table">
<tbody>
<tr>
<th>Feature</th>
<th>Android</th>
<th>Chrome for Android</th>
<th>Firefox Mobile (Gecko)</th>
<th>IE Mobile</th>
<th>Opera Mobile</th>
<th>Safari Mobile</th>
</tr>
<tr>
<td>Basic support</td>
<td>5.1</td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td>26.0 (26)</td>
<td><span style="color: rgb(255, 153, 0);" title="Compatibility unknown; please update this.">?</span></td>
<td><span style="color: rgb(255, 153, 0);" title="Compatibility unknown; please update this.">?</span></td>
<td>10</td>
</tr>
</tbody>
</table>
</div>
</div>
<h2 id="See_also" name="See_also">相关链接</h2>
<ul>
<li><code><a href="/en-US/docs/Web/JavaScript/Reference/Statements/function*">function*</a></code></li>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Iterators_and_Generators">Iterators and generators</a></li>
</ul>
</article>