scope of variables in JavaScript callback functions

Question

I expected the code below to alert \"0\" and \"1\", but it alert \"2\" twice. I don\'t understand the reason. Don\'t know if it is a problem of jQuery. Also, please help me

Answer 1

What's occurring here is your AJAX request $.get is completing after the loop has completed. Because of this, i ends up being the final variable it's set to when the iterations complete, being 2. This is just a weird JavaScript gotcha, and has nothing to do with jQuery.

One thing you can do is queue up these calls asynchronously so that iteration halts until the current AJAX request completes. If you don't want to do that, you can capture the variable i in a function closure in each iteration.

Something like this:

for ( var i = 0; i < 2; i++ )
    (function(iter){
        $.get('http://www.google.com/', function(){
            alert( iter );
        });
    })(i); // Capture i