JS data structures - Stack

stack.js

'use strict';

function Node(item) {
  this.value = item;
  this.next = null;
}

function Stack() {
  this.items = null;
}

Stack.prototype.push = function (item) {
  var node = new Node(item);
  if (this.items === null) {
    this.items = node;
  } else {
    node.next = this.items;
    this.items = node;
  }
};

Stack.prototype.peek = function () {
  return this.items.value;
};

Stack.prototype.pop = function () {
  if (this.items === null) {
    throw new Error('out of range');
  }
  var val = this.items.value;
  this.items = this.items.next;
  return val;
};