How to implement batch request? How to user $.Deferred() to handle batch request limit? How to handle batch request collision?

gistfile1.js

/**
 * If you have a widget on a page.
 */
 
var FacebookWidget = function (userName) {
  this.username = userName;
  this.user = new User(userName);
  this.friends = new FriendList(userName);
  this.activities = new ActivityList(userName);
}

var Limin = new FacebookWidget('limin');
// fetch user info 
Limin.user.fetch();
// fetch friends info
limin.friends.fetch();
// fetch activity info
limin.activities.fetch();
// display all Limin's info
Limin.show();

gistfile2.js

/**
 * Assume each model fetch() function return a Deferred Object,
 * How can we display all the info together?
 */
var dfds = [];
dfds.push( Limin.user.fetch() );
dfds.push( limin.friends.fetch() );
dfds.push( limin.activities.fetch() );

$.when(dfds).done(function (data) {
  Limin.user.set(data[0]);
  Limin.friends.set(data[1]);
  Limin.activities.set(data[2]);
  Limin.show();
});

gistfile3.js

/**
 * What if we can minimize request by batching them together?
 */
API.startBatch();
// fetch user info 
Limin.user.fetch(API);
// fetch friends info
limin.friends.fetch(API);
// fetch activity info
limin.activities.fetch(API);
// display all Limin's info
API.endBatch();

function API = function () {
  this.inBatch = false;
  this.requests = [];
};

API.prototype.startBatch = function () {
  this.inBatch = true;
}

API.prototype.endBatch = function () {
  var self = this;
  $.ajax({
    type : 'GET',
    url : 'http://facebook.com/batch',
    data : this.requests.serialize()
  })
  .done(function (data) {
    _(self.requests).foreach(function (request, index) {
      request.resolve(data[index]);
    });
  });
  this.inBatch = false;
}

gistfile4.js

/**
 * What if the batch request has limit to 2.
 */

function API = function () {
  this.inBatch = false;
  this.requests = [];
  this.limit = 2;
};

API.prototype.startBatch = function () {
  this.inBatch = true;
}

API.prototype.endBatch = function () {
  var self = this;
  var batchNum = Math.ceiling(this.requests.length/2);
  var batchDfds = [];
  for (var i=0; i<batchNum; i++) {
    var dfd = $.Deferred();
    var sendRequests = Array.prototype.slice.call(this.requests, i, i*2-1);
    $.ajax({
      type : 'GET',
      url : 'http://facebook.com/batch',
      data : sendRequests.serialize()
    })
    .done(function (data) {
      dfd.resolve(data);
    });
    batchDfds.push(dfd);
  }
  this.inBatch = false;
  $.when(batchDfds).done(function (data) {
    var results = [];
    _(data).foreach(function(d) {
      results = _.union(results, d);
    });
    _(self.requests).foreach(function (request, index) {
      request.resolve(results[index]);
    });
  });
}

gistfile5.js

/**
 * What if you have 2 widges on the save page?
 */
var Limin = new FacebookWidget('limin');
var Mike = new FacebookWidget('mike');

// fetch Limin's info
API.startBatch();
Limin.user.fetch(API);
limin.friends.fetch(API);
limin.activities.fetch(API);
API.endBatch();

// fetch Mike's info
API.startBatch();
mike.user.fetch(API);
mike.friends.fetch(API);
mike.activities.fetch(API);
API.endBatch();

// How to handle batch collision