Returning value from AJAX call

Returning value from AJAX call

Basically, im trying to write a script that uses AJAX to verify if a username exists. Depending on the response from the AJAX call, it should return true or false. I know I can accomplish this by doing async:false, but thats a no no.

Heres a basic version of the script: 
  1. function  whatever (username) {

        var result = true;

        $.get( "/account/check_username/" + username, function ( response ) {
            if($.trim( response ) == 'Exists') {
                result = false;
            }
        } );
        
        return result;
    }
Anyway to have it set result to false? I know since its Async, the ajax call, the function returns the result variable before the ajax call is complete.

A friend of mine gave me a hint saying I could use a deferred promise, but I havent been able to figure it out.