dfd.js

// assumes Q.js has been loaded and available as Q
function ajaxCall(){
  var dfd = Q.defer(),
      data = getData({
        success: function(response){
          dfd.resolve(response);
        },
        error: function(error){
          dfd.reject(error);          
        }
      });      
  return dfd.promise;
}

var loadData = ajaxCall(); 

/* loadData returns a promise, and promises respond to .then() */
loadData
  .then(function(data){
    // do stuff with the data
  })
  .fail(fn)