gistfile1.js

sinon.FakeXMLHttpRequest = (function () {
    // ...

    function FakeXMLHttpRequest() {
        this.readyState = FakeXMLHttpRequest.UNSENT;
        this.requestHeaders = {};
        this.requestBody = null;
        this.status = 0;
        this.statusText = "";
        this.eventListeners = {};

        if (typeof FakeXMLHttpRequest.onCreate == "function") {
            FakeXMLHttpRequest.onCreate(this);
        }
    }

    var Event = function Event() {};

    sinon.extend(Event.prototype, {
      initEvent: function(type, bubbles, cancelable) {
        this.type = type;
        this.bubbles = bubbles;
        this.cancelable = cancelable;
      },
      stopPropagation: function() {
      },
      preventDefault: function() {
      }
    });

    // ...

    sinon.extend(FakeXMLHttpRequest.prototype, {
        // ...

        addEventListener: function addEventListener(event, listener, useCapture) {
          var listeners = this.eventListeners[event];
          if(!listeners){
            listeners = this.eventListeners[event] = [];
          }
          listeners.push(listener);
        },

        removeEventListener: function removeEventListener(event, listener, useCapture) {
          var listeners = this.eventListeners[event];
          if(listeners) {
            var index = listeners.indexOf(listener);
            if(index != -1) {
              listeners.splice(index, 1);
            }
          }
        },

        dispatchEvent: function dispatchEvent(event) {
          var listeners = this.eventListeners[event.type];
          if(listeners) {
            for(var i = 0; i < listeners.length; i++) {
              listeners[i](event); // TODO shouldn't this implement handleEvent() ?
            }
          }
        },

        readyStateChange: function readyStateChange(state) {
            this.readyState = state;

            if (typeof this.onreadystatechange == "function") {
                this.onreadystatechange();
            }

            var event = new Event();
            event.initEvent('readystatechange');
            this.dispatchEvent(event);
        },

        // ...