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---
title: break
slug: Web/JavaScript/Reference/Statements/break
tags:
- JavaScript
- Statement
translation_of: Web/JavaScript/Reference/Statements/break
---
<div>
<div>{{jsSidebar("Statements")}}</div>
</div>
<p><strong>break 语句</strong>中止当前循环，{{jsxref("Statements/switch", "switch")}}语句或{{jsxref("Statements/label", "label")}} 语句，并把程序控制流转到紧接着被中止语句后面的语句。</p>
<h2 id="语法">语法</h2>
<pre class="syntaxbox notranslate"><code>break [label];</code></pre>
<dl>
<dt><code>label</code> {{可选}}</dt>
<dd>与语句标签相关联的标识符。如果 break 语句不在一个循环或 {{jsxref("Statements/switch", "switch")}} 语句中，则该项是必须的。</dd>
</dl>
<h2 id="描述">描述</h2>
<p><code>break</code>语句包含一个可选的标签，可允许程序摆脱一个被标记的语句。<code>break</code>语句需要内嵌在引用的标签中。被标记的语句可以是任何 {{jsxref("Statements/block", "块")}}语句；不一定是循环语句。</p>
<p>break语句不能在function函数体中直接使用，break语句应嵌套在要中断的当前循环、switch或label语句中。</p>
<h2 id="示例">示例</h2>
<h3 id="break_in_while_loop">break in while loop</h3>
<p>下面的函数里有个 <code>break</code> 语句，当 <code>i</code> 为 3 时，会中止 {{jsxref("Statements/while", "while")}} 循环，然后返回 3 * <code>x</code> 的值。</p>
<pre class="brush: js notranslate"><code class="language-js"><span class="keyword token">function</span> <span class="function token">testBreak</span><span class="punctuation token">(</span>x<span class="punctuation token">)</span> <span class="punctuation token">{</span>
<span class="keyword token">var</span> i <span class="operator token">=</span> <span class="number token">0</span><span class="punctuation token">;</span>
<span class="keyword token">while</span> <span class="punctuation token">(</span>i <span class="operator token"><</span> <span class="number token">6</span><span class="punctuation token">)</span> <span class="punctuation token">{</span>
<span class="keyword token">if</span> <span class="punctuation token">(</span>i <span class="operator token">==</span> <span class="number token">3</span><span class="punctuation token">)</span> <span class="punctuation token">{</span>
<span class="keyword token">break</span><span class="punctuation token">;</span>
<span class="punctuation token">}</span>
i <span class="operator token">+</span><span class="operator token">=</span> <span class="number token">1</span><span class="punctuation token">;</span>
<span class="punctuation token">}</span>
<span class="keyword token">return</span> i <span class="operator token">*</span> x<span class="punctuation token">;</span>
<span class="punctuation token">}</span></code></pre>
<h3 id="break_in_switch_statements">break in switch statements</h3>
<p>在下面的代码中， <code>break</code> 使用在 {{jsxref("Statements/switch", "switch")}} 语句中，当遇到匹配到case后，就会执行相应的代码并中断循环体。</p>
<pre class="notranslate">const food = "sushi";
switch (food) {
case "sushi":
console.log("Sushi is originally from Japan.");
break;
case "pizza":
console.log("Pizza is originally from Italy.");
break;
default:
console.log("I have never heard of that dish.");
break;
}</pre>
<h3 id="break_in_labeled_blocks">break in labeled blocks</h3>
<p>下面的代码中一起使用 <code>break</code> 语句和被标记的块语句。一个 <code>break</code> 语句必须内嵌在它引用的标记中。注意，<code>inner_block</code> 内嵌在 <code>outer_block</code> 中。</p>
<pre class="brush:js;highlight:[1,3,5]; notranslate">outer_block:{
inner_block:{
console.log ('1');
break outer_block; // breaks out of both inner_block and outer_block
console.log (':-('); // skipped
}
console.log ('2'); // skipped
}
</pre>
<h3 id="break_in_labeled_blocks_that_throw">break in labeled blocks that throw</h3>
<p>下面的代码同样使用了 <code>break</code> 语句和被标记的块语句，但是产生了一个语法错误，因为它的 <code>break</code> 语句在 <code>block_1</code> 中，但是引用了 <code>block_2</code>。<code>break</code> 语句必须内嵌在它引用的标签中。</p>
<pre class="brush:js;highlight:[1,3,6]; notranslate">block_1:{
console.log ('1');
break block_2; // SyntaxError: label not found
}
block_2:{
console.log ('2');
}
</pre>
<h3 id="break_within_functions">break within functions</h3>
<p>在下面的代码同样会产生SyntaxError，因为它并没被正确的使用在循环、switch或label语句中。</p>
<pre class="notranslate">function testBreak(x) {
var i = 0;
while (i < 6) {
if (i == 3) {
(function() {
break;
})();
}
i += 1;
}
return i * x;
}
testBreak(1); // SyntaxError: Illegal break statement
</pre>
<pre class="notranslate">block_1: {
console.log('1');
( function() {
break block_1; // SyntaxError: Undefined label 'block_1'
})();
}</pre>
<h2 id="规范">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>{{SpecName('ES1')}}</td>
<td>{{Spec2('ES1')}}</td>
<td>Initial definition. Unlabeled version.</td>
</tr>
<tr>
<td>{{SpecName('ES3')}}</td>
<td>{{Spec2('ES3')}}</td>
<td>Labeled version added.</td>
</tr>
<tr>
<td>{{SpecName('ES5.1', '#sec-12.8', 'Break statement')}}</td>
<td>{{Spec2('ES5.1')}}</td>
<td></td>
</tr>
<tr>
<td>{{SpecName('ES6', '#sec-break-statement', 'Break statement')}}</td>
<td>{{Spec2('ES6')}}</td>
<td></td>
</tr>
<tr>
<td>{{SpecName('ESDraft', '#sec-break-statement', 'Break statement')}}</td>
<td>{{Spec2('ESDraft')}}</td>
<td></td>
</tr>
</tbody>
</table>
<h2 id="浏览器兼容">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.statements.break")}}</p>
<h2 id="See_also" name="See_also">相关链接</h2>
<ul>
<li>{{jsxref("Statements/continue", "continue")}}</li>
<li>{{jsxref("Statements/label", "label")}}</li>
<li>{{jsxref("Statements/switch", "switch")}}</li>
</ul>
|
