queue.js

var Node = function(value) {
  this.prevNode  = null;
  this.value     = value;
}

var Queue = function() {
  this.first    = null;
  this.last     = null;
  this.length   = 0;
}

Queue.prototype.push = function(value) {
  var node = new Node(value);
  
  if(this.length !== 0) {
    this.last.prevNode  = node;
    this.last           = node;
  } else {
    this.last           = node;
    this.first          = node;
  }
  this.length++;
}

Queue.prototype.pop = function() {
  if(this.length === 0)
    return null;
  else if(this.length === 1) {
    var node    = this.first;
    this.first  = null;
    this.last   = null;
    this.length--;
    return node.value;
  }
  
  var node      = this.first;
  this.first    = this.first.prevNode;
  this.length--;
  return node.value;
}