stack.js

// Stack operations will always have a time complexity of O(1) regardless the size of the stack

var Stack = function() {
  this.count = 0;
  this.storage = {};
}


Stack.prototype = (function() {
return {
  size: size,
  push: push,
  pop: pop,
  peek: peek,
  empty: empty,
  swap: swap
}

function size() {
  return this.count;
}

function push(value) {
  this.storage[this.count] = value;
  this.count++;
}

function pop() {
  if (this.count === 0) {
    return undefined;
  }

  this.count--;
  var result = this.storage[this.count];
  delete this.storage[this.count];
  return result;
}

function peek() {
  return this.storage[this.count - 1];
}

function empty() {
  return this.count === 0;
}

function swap() {
  var last = this.storage[this.count - 1];
  var oneBeforeLast = this.storage[this.count - 2];
  this.storage[this.count - 2] = last;
  this.storage[this.count - 1] = oneBeforeLast;
}
})();