Firefox SDK Callback Registry

//main.js - our background script
var data = require("sdk/self").data;
var tabs = require('sdk/tabs');
var Requester = require("sdk/request");
tabs.on('ready', function(tab) {
 //Listens for "GET" messages from the content script
 worker.port.on("GET", function(params) {
  var req = new Requester.Request({
   url: params.url,
   onComplete: function (response) {
    //get the key of the callback stashed on the content script,
    //based on whether or not the request was successful
    var callbackKey = (response.status == 200) ? params.sKey : params.errKey||null;

    //send a message back to the appropriate listener on the content script
    worker.port.emit('ajaxResponse', {responseText: response.text,
       callbackKey: callbackKey});
   }
  });
  req.get();
 });
});
//bootstrap.js - acts as a bridge between the background script and the content script
(function() {

 // register callbacks that need to be executed on the
 // response from the background script
 var callbacks = {};
 // Receives an AJAX response and a callback ID.
 // Retrieves the callback via ID and executes it,
 // passing the response as a parameter
 self.port.on("ajaxResponse", function(response) {
  if ((response.callbackKey) && callbacks[response.callbackKey]) {
   //Retreive the callback and execute
   callbacks[response.callbackKey](response);
   delete callbacks[response.callbackKey];
  }
 });

 var smallRandom = function() {
  return ('' + Math.random()).substring(2);
 };

 AJAX = function(params) {
  params.method = params.method||'GET';

  //in case method is defined, upper case it for
  //consumption by the background API
  params.method = params.method.toUpperCase();

  if (params.onerror) {
   // make sure the key for the callback is fairly unique
   var callbackKey = smallRandom();
   callbacks[callbackKey] = params.onerror;
   params.errKey = callbackKey;
  }

  //Functions can't be passed to the background page.
  //Register the callback, retrieve by key, then call
  //so as not to lose its scope.
  if (params.onload) {
  // make sure the key for the callback is fairly unique
   var callbackKey = smallRandom();
   callbacks[callbackKey] = params.onload;
   params.sKey = callbackKey;
  }

  //now send the request message to the background script
  self.port.emit(params.method, params);
 }
})();