jsonp.js

// JSONP.Request for Prototype
// based on: http://github.com/kangax/protolicious/blob/master/get_json.js
JSONP = { count: 0 };
JSONP.Request = Class.create({
  initialize: function(url, options) {
    this.options = {
      timeoutInSeconds: 5,
      onSuccess: Prototype.emptyFunction,
      onFailure: Prototype.emptyFunction
    };
    Object.extend(this.options, options || { });

    this.request(url, this.options.onSuccess, this.options.onFailure);
  },
  request: function(url, callbackfn, failurefn) {
    this.global = window;
    this.script = document.createElement('script')
    this.token = '__jsonp'+JSONP.count;        
    this.head = $$('head')[0];
        
    this.timeoutId = this.onTimeOut.bind(this).delay(this.options.timeoutInSeconds);

    // e.g.: global[__jsonp0] = callbackfn function(){}
    this.global[this.token] = callbackfn;
    
    // look for "?" parameter in the url, replace it with new unique callback
    this.script.src = url.replace( /\?(&|$)/,  this.token + '$1'); // the '$1' is to add back in & that are excluded in the regex

    // clean up on load: remove script tag, null script variable and delete global callback function
    this.script.onload = this.onScriptLoad.bind(this);
    this.head.appendChild(this.script);

    // callback name should be unique
    JSONP.count++;
  },

  onScriptLoad: function() {
    this.cleanup();
  },

  onTimeOut: function() {
    this.script.onload = null;
    this.cleanup();
    if (this.options.onFailure) this.options.onFailure();
  },

  cleanup: function() {
    clearTimeout(this.timeoutId);
    this.timeoutId = null;
    this.script.remove();
    this.script = null;
    delete this.global[this.token]; // callback has served it's purpose -- remove it
  }
});

// EXAMPLE
// new JSONP.Request(
//   "http://api.flickr.com/services/feeds/photos_public.gne?tags=cat&tagmode=any&format=json&jsoncallback=?",
//   {
//     timeoutInSeconds: 5,
//     onSuccess: function(data) {
//       console.log(data.items.pluck('title').join('\n'))
//     },
//     onFailure: function() {
//       console.log("Error loading JSONP.Request");
//     }
//   }
// );