Stack.js

// implement a stack using linkedLists
var LinkedList = require('./LinkedList');

var Stack = function() {
  this.top = null;
};

Stack.prototype.push = function(value) {
  var node = new LinkedList(value);
  node.next = this.top;
  this.top = node;
};

Stack.prototype.pop = function() {
  var popped = this.top;
  if (this.top !== null) {
    this.top = this.top.next;
  }
  return popped.value;
};

Stack.prototype.peek = function() {
  return this.top !== null ? this.top.value : null;
};

Stack.prototype.isEmpty = function() {
  return this.top === null;
};

module.exports = Stack;

/* TEST */

// var s = new Stack();
// s.push('a');
// s.push('b');
// s.push('c');
// console.log(s.pop(), 'c');
// console.log(s.peek(), 'b');
// console.log(s.pop(), 'b');
// console.log(s.pop(), 'a');
// console.log(s.isEmpty(), true);