SOURCE

//es5定义类的方式
var Stack = function() {
  var items = [];
  //向栈顶添加元素
  this.push = function(element) {
    items.push(element);
  },
  //获取元素
  this.getItems = function() {
    return items
  },
  //拿出元素
  this.pop = function() {
    return items.pop()
  },
  //获取栈顶元素
  this.peek = function() {
    return items[items.length - 1]
  },
  //判断是否为空
  this.isEmpty = function() {
    return items.length == 0
  },
  //清除元素
  this.clear = function() {
    return items = [];
  },
  //获取个数
  this.size = function() {
    return items.length;
  }
}

//栈实现余数法