js closures and loops

巴扎黑
Release: 2016-12-10 09:15:16
Original
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function box(){ var arr = []; for(var i=0;i<5;i++){ arr[i]=function(){ return i; } } return arr; } var b = box(); console.log(b.length); for(var i=0;i
        
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The above code will print out 5 5

because b[i]() calls an anonymous function, but the anonymous function does not execute itself, so by the time it is called, box() has already been executed. . . .

Change the following:

function box(){ var arr = []; for(var i=0;i<5;i++){ arr[i]=( function(num){ console.log("ccc="+num) return num; } )(i) } return arr; } var b = box(); console.log(b.length); for(var i=0;i
        
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Execution result:

Html code

num=0 num=1 num=2 num=3 num=4 5 0 1 2 3 4
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