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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 to edit title and tags of this post if they are inaccurate.
<html> <head> <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"></script> <script type="text/javascript"> $(function() { for (var i=0; i<2; i++) { $.get('http://www.google.com/', function() { alert(i); }); } }); </script> </head> <body> </body> </html> 
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JavaScript variables have only two scopes. Global Variables − A global variable has global scope which means it can be defined anywhere in your JavaScript code. Local Variables − A local variable will be visible only within a function where it is defined. Function parameters are always local to that function.
When a callback function completes execution, it returns any return value that it might have to the DataBlade API, which invoked it.
You're sharing the single i variable among all of the callbacks.
Because Javascript closures capture variables by reference, the callbacks will always use the current value of i. Therefore, when jQuery calls the callbacks after the loop executes, i will always be 2.
You need to reference i as the parameter to a separate function.
For example:
function sendRequest(i) { $.get('http://www.google.com/', function() { alert(i); }); } for (var i = 0; i < 2; i++) { sendRequest(i); } This way, each callback will have a separate closure with a separate i parameter.
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Alternative to SLaks' answer
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