JSON/Swiffy PxLoader extension

SwiffyLoader.js

// @depends PxLoader.js
/**
 * PxLoader plugin to load swiffy
 */

function PxLoaderSwiffy(name, tags, priority) {
  var self = this,
      loader = null,
      complete = false;

  this.tags = tags;
  this.priority = priority;
  var data = null;

  this.start = function(pxLoader) {
    // we need the loader ref so we can notify upon completion
    loader = pxLoader;

    var xhr = new XMLHttpRequest();
    xhr.open("GET", name, false);
    xhr.onreadystatechange = function() {
      if (xhr['readyState'] !== 4)  { return; }
      if (xhr['status'] !== 200) {
        loader.onError(self);
        return;
      }
      
      var serverResponse = xhr['responseText'];
      try {
        data = JSON.parse(serverResponse);
        loader.onLoad(self);
      } catch (e) {
        loader.onError(self);
      }
    }
    xhr.send(null);
  };

  // called by PxLoader to check status of image (fallback in case
  // the event listeners are not triggered).
  this.checkStatus = function() {
    if (complete) {
      loader.onLoad(self);
    }
  };

  // called by PxLoader when it is no longer waiting
  this.onTimeout = function() {
    if (complete) {
      loader.onLoad(self);
    } else {
      loader.onTimeout(self);
    }
  };

  // returns a name for the resource that can be used in logging
  this.getName = function() {
    return name;
  };

  this.getData = function() {
    return data;
  }
}

// add a convenience method to PxLoader for adding an image
PxLoader.prototype.addSwiffy = function(name, tags, priority) {
    var swiffyLoader = new PxLoaderSwiffy(name, tags, priority);
    this.add(swiffyLoader);

    // return the img element to the caller
    return swiffyLoader.name;
};