Question

Consider this code example:

var source = null;

$.ajax({
    [...],
    success:function(data)
    {
        source = data;
        alert(source);
    }
});

alert(source);

Now: inside of the success handler, everything is fine, I get the correct data from the webservice and everything is just great. But as soon as JS leaves the $.ajax and is done with it the variable source is null again.

Tell me why. It must be some JavaScript specfic stuff I’m not familiar with. :/

Answer 1

It is probably because you are forgetting AJAX is asynchronous. The source variable will be undefined until the success callback is completed.

Doing alert(source) beneath that code (outside of the $.ajax()) is almost guaranteed to be undefined.