facebook.loadonce.js

/*global $ */

/*

 _______  _______  _______  _______  _______  _______  _______  ___   _
|       ||   _   ||       ||       ||  _    ||       ||       ||   | | |
|    ___||  |_|  ||       ||    ___|| |_|   ||   _   ||   _   ||   |_| |
|   |___ |       ||       ||   |___ |       ||  | |  ||  | |  ||      _|
|    ___||       ||      _||    ___||  _   | |  |_|  ||  |_|  ||     |_
|   |    |   _   ||     |_ |   |___ | |_|   ||       ||       ||    _  |
|___|    |__| |__||_______||_______||_______||_______||_______||___| |_|
 ___      _______  _______  ______   _______  __    _  _______  _______
|   |    |       ||   _   ||      | |       ||  |  | ||       ||       |
|   |    |   _   ||  |_|  ||  _    ||   _   ||   |_| ||       ||    ___|
|   |    |  | |  ||       || | |   ||  | |  ||       ||       ||   |___
|   |___ |  |_|  ||       || |_|   ||  |_|  ||  _    ||      _||    ___|
|       ||       ||   _   ||       ||       || | |   ||     |_ |   |___
|_______||_______||__| |__||______| |_______||_|  |__||_______||_______|


Facebook.loadOnce is a simple wrapper for the official Facebook JS SDK for promise-based lazy-loading.


  1. Whenever you want to for example initialize a Facebook button:
  
  Facebook.setCulture("nl-nl");
  Facebook.loadOnce().done(function (FB) {
                            FB.XFBML.parse();
                          });


  2. When you call loadOnce again it will NOT load again but with it WILL trigger 
     the done handler immediately:

  Facebook.loadOnce().done(function (FB) {
                            FB.XFBML.parse();
                          });

  Note that setCulture() should be called once, before the first time loadOnce() is used. 
  If you forget this (or do this twice), an exception will be thrown.


  3. Also, since Facebook.loadOnce returns a Promise object, you can use the full 
  Promise API, including chaining asynchronous calls:

  Facebook.loadOnce().then(function () {
    return $.post("/dummy", { some: "data" });
  })
  .then(function() {
    return $("#dialog").animate({ opacity : 1});
  })
  .done(function () {
    console.log("all done!");
  });

*/

var Facebook = (function() {
  "use strict";

  var _loadingStarted, _culture;

  window.fbAsyncInit = function() {
    if (window.FB)
      _loadingStarted.resolve(window.FB);
    else
      _loadingStarted.reject(); // shouldn't happen! probably means a bug in FB
  };

  function _load() {
    _loadingStarted = $.Deferred();

    // Load the SDK Asynchronously
    (function (d) {
      var js, id = 'facebook-jssdk', ref = d.getElementsByTagName('script')[0];
      if (d.getElementById(id)) { return; }
      js = d.createElement('script');
      js.id = id;
      js.async = true;
      js.src = "//connect.facebook.net/"+_culture+"/all.js";
      ref.parentNode.insertBefore(js, ref);
    } (document));
  }

  return {
    setCulture: function(culture) {
      if (_culture)
        throw new Error("Culture cannot be changed after first set");

      _culture = culture;
    },
    loadOnce : function() {
      if (!_culture)
        throw new Error("Culture should be set before first load");

      if (!_loadingStarted)
        _load();

      return _loadingStarted.promise();
    }
  };

}());