栈

1. 栈是后进先出

stack: function () {
        this.dataStore = [];    //初始化为空
        this.top = 0;           //记录栈顶位置
        this.pop = pop;         //出栈
        this.push = push;       //入栈
        this.peek = peek;       //查看栈顶元素
        this.length = length;   //查看栈内元素总数
        this.clear = clear;     //清空栈
    }

const _items = Symbol('stackItems');

class Stack {
  constructor() {
    this[_items] = [];
  }
//添加元素到栈顶
  push(element) {
    this[_items].push(element);
  }
// 从栈移除元素,移出的是最后添加进去的元素
  pop() {
    return this[_items].pop();
  }
// 查看栈顶的元素
  peek() {
    return this[_items][this[_items].length - 1];
  }
// 栈为空则返回 true ,非空 则返回 false
  isEmpty() {
    return this[_items].length === 0;
  }
// 返回栈的长度
  size() {
    return this[_items].length;
  }
// 清空栈
  clear() {
    this[_items] = [];
  }

  print() {
    console.log(this.toString());
  }

  toString() {
    return this[_items].toString();
  }
}

const stack = new Stack();//初始化stack类
const objectSymbols = Object.getOwnPropertySymbols(stack);
console.log(objectSymbols.length); // 1
console.log(objectSymbols); // [Symbol()]
console.log(objectSymbols[0]); // Symbol()
stack[objectSymbols[0]].push(1);
stack.print(); // 5, 8, 1