Analysis of label statement usage in JavaScript_javascript skills-JS Tutorial-php.cn

Analysis of label statement usage in JavaScript_javascript skills

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Release： 2016-05-16 16:15:03

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This article analyzes the usage of tag statements in JavaScript with examples. Share it with everyone for your reference. The specific analysis is as follows:

I was watching w3school recently, and then I saw the js part,

<!DOCTYPE html>
<html>
<body>
<script>
cars=["BMW","Volvo","Saab","Ford"];
list:
{
document.write(cars[0] + "<br>"); 
document.write(cars[1] + "<br>"); 
document.write(cars[2] + "<br>"); 
break list;
document.write(cars[3] + "<br>"); 
document.write(cars[4] + "<br>"); 
document.write(cars[5] + "<br>"); 
}
</script>
</body>
</html>

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Seeing that list: I feel a little weird, and then it says

JavaScript Tag

As you saw in the chapter on switch statements, JavaScript statements can be tagged.

To mark a JavaScript statement, precede it with a colon:

label:
statements

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The break and continue statements are simply statements that break out of a block of code.

Syntax:

break labelname; 

continue labelname;

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continue statements (with or without label references) can only be used within loops.
The break statement (without label reference) can only be used in a loop or switch.
The break statement can be used to break out of any block of JavaScript code, referenced by a tag:

I didn’t pay attention to it at first, but then Baidu marked the javascript statement and read a blog that said this. Let’s learn from it here:

For example:

parser:
 while(token != null) {
 //Code omitted here
}

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By labeling a statement, you can give the statement a name, so that you can use this name to refer to it anywhere in the program. You can label any statement,

But the marked statements are usually those loop statements, namely while, do/while, for and for/in statements. Usually the loops are named, and the break statement and continue statement can be used

Exit the loop or an iteration of the loop.

For example:

<script type="text/javascript"> 
  outerloop: 
   for (var i = 0; i < 10; i++) 
   { 
     innerloop:  
     for (var j = 0; j < 10; j++) 
      { 
        if (j > 3) 
        { 
          break; 
        } 
        if (i == 2) 
        { 
          break innerloop; 
        } 
        if (i == 4) 
        { 
          break outerloop; 
        } 
        document.write("i=" + i + " j=" + j + "<br>"); 
      } 
   } 
</script>

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After seeing this example, I understood list: clearly. I hope this article will be helpful to everyone’s JavaScript programming design.