break 语句中止当前循环，`switch`语句或`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。

## 语法

    break [label];

`label`
  可选。与语句标签相关联的标识符。如果 break 语句不在一个循环或 `switch` 语句中，则该项是必须的。

## 描述

`break`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。`break`语句需要内嵌在引用的标签中。被标记的语句可以是任何 `块`语句；不一定是循环语句。

## 示例

下面的函数里有个 `break` 语句，当 `i` 为 3 时，会中止 `while` 循环，然后返回 3 * `x` 的值。

    function testBreak(x) {
      var i = 0;

      while (i < 6) {
        if (i == 3) {
          break;
        }
        i += 1;
      }

      return i * x;
    }

下面的代码中一起使用 `break` 语句和被标记的块语句。一个 `break` 语句必须内嵌在它引用的标记中。注意，`inner_block` 内嵌在 `outer_block` 中。

    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
    }

下面的代码同样使用了 `break` 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 `break` 语句在 `block_1` 中，但是引用了 `block_2`。`break` 语句必须内嵌在它引用的标签中。

    block_1:{
      console.log ('1');
      break block_2;            // SyntaxError: label not found
    }

    block_2:{
      console.log ('2');
    }

## 规范

Specification | Status | Comment
--- | --- | ---
ECMAScript 1st Edition (ECMA-262) | Standard | Initial definition. Unlabeled version.
ECMAScript 3rd Edition (ECMA-262) | Standard | Labeled version added.
ECMAScript 5.1 (ECMA-262) Break statement | Standard |
ECMAScript 2015 (6th Edition, ECMA-262) Break statement | Standard |
ECMAScript Latest Draft (ECMA-262) Break statement | Draft |

## 浏览器兼容

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

Update compatibility data on GitHub

| Desktop | Mobile | Server
| Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | Android webview | Chrome for Android | Edge Mobile | Firefox for Android | Opera for Android | Safari on iOS | Samsung Internet | Node.js
`break` | Chrome Full support Yes | Edge Full support Yes | Firefox Full support 1 | IE Full support Yes | Opera Full support Yes | Safari Full support Yes | WebView Android Full support Yes | Chrome Android Full support Yes | Edge Mobile Full support Yes | Firefox Android Full support 4 | Opera Android Full support Yes | Safari iOS Full support Yes | Samsung Internet Android Full support Yes | nodejs Full support Yes

### Legend

Full support
  Full support

## 相关链接

- `continue`
- `label`
- `switch`