Queue callbacks in javascript

queue.js

/*
 * queue.js allow you to run async callbacks in serial.
 */

var Queue = {
  callbacks: [],
  idle: true,

  // Queue.add(function() {});
  // Used to add a new function to the callback queue
  add: function() {
    var cb = arguments[0];

    if(window.console) console.log('Queue.add( function )');

    Queue.callbacks.push(function() {
      if(window.console) console.log('Queue.shift( function )');
      Queue.callbacks.shift();
      cb();
      Queue.idle = true;
      Queue.next();
      return true;
    });

    Queue.next();
  },

  // Queue.ajax(url, function(json) {});
  // Used to add a new function to the callback queue which will be fired
  // once $.ajax(url, ...) receives data from the server
  ajax: function() {
    var url = arguments[0][0];
    var cb = arguments[0][1];

    if(window.console) console.log('Queue.ajax(', url, ')');

    Queue.callbacks.push(function() {
      $.ajax({
        url: url,
        success: function(data) {
          if(window.console) console.log('Queue.shift(', url, ')');
          Queue.callbacks.shift();
          cb.call(this, data);
          Queue.idle = true;
          Queue.next();
        }
      });
      return false;
    });

    Queue.next();
  },

  // Queue.next();
  // This is called automatically by the async callbacks in add()
  // and getJSON()
  next: function() {
    if(!Queue.idle) return;
    var cb = Queue.callbacks[0];
    if(!cb) return;
    Queue.idle = cb();
  }
};