JavaScript function that returns AJAX call data

I would like to create a JavaScript function which returns the value of a jQuery AJAX call. I would like something like this.

function checkUserIdExists(userid){
    return $.ajax({
        url: 'theurl',
        type: 'GET',

        cache: false,
        data: {
           userid: userid
        },
        success: function(data){
            return data;
        }
    });
}

I know I can do this by setting async to false but I would rather not.

Answer

With jQuery 1.5, you can use the brand-new $.Deferred feature, which is meant for exactly this.

// Assign handlers immediately after making the request,
// and remember the jqxhr object for this request
var jqxhr = $.ajax({ url: "example.php" })
    .success(function() { alert("success"); })

    .error(function() { alert("error"); })
    .complete(function() { alert("complete"); });

// perform other work here ...

// Set another completion function for the request above
jqxhr.complete(function(){ alert("second complete"); });

Source