If you've written a class in JavaScript that calls a remote service's API, and that remote API offers a callback, how do you get the response back into the instance of the object that made the request?

I'll try to give you a very basic example FOO for making cross domain calls to BAR service which offers a callback. Please ignore the usual security concerns, (I own both servers).

function FOO() {

   this.response = null;
   this.execute = function(url) {

      var script = document.createElement('script');
  script.src = url;
  document.getElementsByTagName('head')[0].appendChild(script); 
   }
   this.catch = function(response) {
        this.response = response;
   }

}


var sample = new FOO();

sample.execute('http://barservices.com/sample/?callback={ plshelphere: this.catch}');

I have a way to make this work, but I'm curious if there is an "accepted approach" here.

Anyone have thoughts for me?