Zdanie break w JavaScript

定义和用法

break 语句退出 switch 语句或循环（for、for ... in、while、do ... while）。

当 break 语句与 switch 语句一起使用时，它会跳出 switch 块。这将停止在块内执行更多代码和/或 case 测试。

在循环中使用 break 语句时，它会中断循环并继续执行循环后的代码（如果有）。

break 语句还可以与可选的标签引用一起使用，以“跳出”任何 JavaScript 代码块（请参阅下面的“更多实例”）。

注释：如果不引用标签，break 语句只能在循环或 switch 中使用。

example

在这个例子中，我们将 for 循环与 break 语句一起使用。

当变量 i 等于 "3" 时退出循环的循环一段代码：

var text = ""
var i;
for (i = 0; i < 5; i++) {
  if (i === 3) {
    break;
  }
  text += "The number is " + i + "<br>";
}

try it yourself

页面下方有更多 TIY 实例。

语法

break;

使用可选的标签引用：

break labelname;

技术细节

JavaScript 版本： ECMAScript 1

更多实例

example

在本例中，我们将 while 循环与 break 语句一起使用。

当变量 i 等于 "3" 时退出循环的循环一段代码：

var text = "";
var i = 0;
while (i < 5) {
  text += "<br>The number is " + i;
  i++;
  if (i === 3) {
    break;
  }
}

try it yourself

example

Jump out of the switch block to ensure that only one case is executed:

var day;
switch (new Date().getDay()) {
  case 0:
    day = "Sunday";
    break;
  case 1:
    day = "Monday";
    break;
  case 2:
    day = "Tuesday";
    break;
  case 3:
    day = "Wednesday";
    break;
  case 4:
    day = "Thursday";
    break;
  case 5:
    day = "Friday";
    break;
  case 6:
    day = "Saturday";
    break;
}

try it yourself

example

Use the break statement with a label reference to "jump out" of a JavaScript code block:

var cars = ["BMW", "Volvo", "Saab", "Ford"];
var text = "";
list: {
  text += cars[0] + "<br>"; 
  text += cars[1] + "<br>"; 
  text += cars[2] + "<br>"; 
  break list;
  text += cars[3] + "<br>"; 
}

try it yourself

example

Use the break statement with a label reference to "jump out" of nested for loops:

var text = "";
var i, j;
Loop1: // The first for loop is marked as "Loop1"
for (i = 0; i < 3; i++) {
text += "<br>" + "i = " + i + ", j = ";
  Loop2: // The second for loop is marked as "Loop2"
  for (j = 0; j < 5; j++) {
    if (j === 2) {
      break Loop1;
    }
    document.getElementById("demo").innerHTML = text += j + " ";
  }
}

try it yourself

browser support

statement Chrome IE Firefox Safari Opera
break support support support support support

related pages

JavaScript Tutorial:Break i continue w JavaScript

JavaScript Tutorial:Pętla for w JavaScript

JavaScript Tutorial:Pętla while w JavaScript

JavaScript Tutorial:JavaScript Switch

JavaScript Reference Manual:Zdanie continue w JavaScript

JavaScript Reference Manual:Zdanie for w JavaScript

JavaScript Reference Manual:Zdanie while w JavaScript

JavaScript Reference Manual:Zdanie switch w JavaScript