[Javascript] Function scope

We have code like:

var numbers = [1,2,3];

for(var i in numbers){

    setTimeout(function(){console.log(numbers[i]);

    }, 0);

}

//

//

//

Note:

1. function block doesn't create scope!

2. setTimeout function run after all the other code finished.

Therefore, before setTimeout get run, for block already exec 3 times and i was set to 2.

Once setTimeout get running, it prints out numbers[i] which is 3.

Now, we change the code to:

var numbers = [1,2,3];

for(var i  in  numbers){

   (function(){

       var j = i;

        setTimeout(function(){

           console.log(numbers[j]);

        })

   })();

}

//

//

//

Note:

1. function does create new scope.

2. the (function(){})() run immedatly.

3. (function(){}) inside for block actually is closure which does remeber the local var value (in our case is var j).

巴特西

[Javascript] Function scope

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