JavaScript 如何打破嵌套的for循环

break语句用于提前退出循环。

可以使用标签与break结合使用，以更精确地控制流程。标签只是一个后面跟着冒号(:)的标识符，应用于语句或一段代码块。

注意: 标签名称与相关循环之间不应有其他语句。

示例-1: 退出嵌套循环

<!DOCTYPE html> 
  
<html> 
  
<head> 
    <title> 
        Break Nested For loop 
    </title> 
</head> 
  
<body> 
    <script type="text/javascript"> 
        <!-- 
        document.write( 
          "Entering the Geeks For Geeks!<br /> "); 
  
        for (var i = 0; i < 5; i++) { 
            document.write( 
              "For Upper Level in GfG : " + i + "<br />"); 
            document.write("<br />") 
  
            for (var j = 0; j < 5; j++) { 
                // Break from the inner loop 
                if (j == 3) break;  
  
                document.write( 
                  "For Deeper Level in GfG : " + j + " <br />"); 
            } 
           // Break from the outer loop 
            if (i == 3) break; 
        } 
        document.write("Exiting the Geeks For Geeks!<br /> "); 
  
    </script> 
</body> 
</html>

输出：

Entering the Geeks For Geeks!
For Upper Level in GfG : 0

For Deeper Level in GfG : 0 
For Deeper Level in GfG : 1 
For Deeper Level in GfG : 2 
For Upper Level in GfG : 1

For Deeper Level in GfG : 0 
For Deeper Level in GfG : 1 
For Deeper Level in GfG : 2 
For Upper Level in GfG : 2

For Deeper Level in GfG : 0 
For Deeper Level in GfG : 1 
For Deeper Level in GfG : 2 
For Upper Level in GfG : 3

For Deeper Level in GfG : 0 
For Deeper Level in GfG : 1 
For Deeper Level in GfG : 2 
Exiting the Geeks For Geeks!

示例-2： 使用标签从嵌套循环中断。

<!DOCTYPE html> 
<html> 
  
<head> 
    <title> 
        Break Nested For loop Using Labels 
    </title> 
</head> 
  
<body> 
    <script type="text/javascript"> 
        <!-- 
        document.write("Entering the Geeks for Geeks!<br /> "); 
        upperloop: // This is the label name          
            for (var i = 0; i < 5; i++) { 
                document.write( 
                   "For Upper Level in GfG : " + i + "<br />"); 
                document.write("<br />"); 
                deeperloop: 
                    for (var j = 0; j < 5; j++) { 
                        // Break from the inner loop 
                        if (j > 3) break;  
                        // Do the same thing 
                        if (i == 2) break deeperloop;  
                        // Break from the outer loop 
                        if (i == 3) break upperloop;  
                        document.write("For Deeper Level in GfG: "
                                       + j + " <br />"); 
                    } 
            } 
        document.write("Exiting the Geeks For Geeks!<br /> "); 
  
    </script> 
</body> 
  
</html>

输出:

Entering the Geeks for Geeks!
For Upper Level in GfG : 0

For Deeper Level in GfG: 0 
For Deeper Level in GfG: 1 
For Deeper Level in GfG: 2 
For Deeper Level in GfG: 3 
For Upper Level in GfG : 1

For Deeper Level in GfG: 0 
For Deeper Level in GfG: 1 
For Deeper Level in GfG: 2 
For Deeper Level in GfG: 3 
For Upper Level in GfG : 2

For Upper Level in GfG : 3

Exiting the Geeks For Geeks!