JavaScript Data Structure - Queue

queue.js

var Queue = function() {
  this.data = [];
};

Queue.prototype.size = function() {
  return this.data.length;
}

Queue.prototype.empty = function() {
  return this.size() === 0;
}

Queue.prototype.enqueue = function(val) {
  this.data.unshift(val);
};

Queue.prototype.dequeue = function() {
  return !this.empty() ? this.data.pop() : -1;
};

Queue.prototype.front = function() {
  return !this.empty() ? this.data[0] : -1;
};

Queue.prototype.back = function() {
  return !this.empty() ? this.data[this.size()-1] : -1;
};