SOURCE

class Stack{//栈——LIFO后进先出
    constructor(){
        this.count = 0;
        this.items = {};
    }

    push=(element)=>{
        //添加新元素到栈顶
        this.items[this.count] = element;
        this.count++;
    }

    pop=()=>{
        //移除最后一个元素
        if(this.isEmpty()){
            return undefined
        }
        this.count--;
        const result = this.items[this.count];
// delete 操作符用于删除对象的某个属性；如果没有指向这个属性的引用，那它最终会被释放。
        delete this.items[this.count];
        return result;
    }

    peek=()=>{
        //查看栈顶元素
         if (this.isEmpty()) {
            return undefined;
        }
        return this.items[this.count - 1];
    }

    isEmpty=()=>{
        //检查栈是否为空
        return this.count ===0;
    }

    size=()=>{
        return this.count;
    }

    clear=()=>{
        this.items = {};
        this.count = 0;
        //或者
        /**
         * while (!this.isEmpty()) {
                this.pop();
            }
         */
    }

    show=()=>{
        return JSON.stringify(this)
    }

}

//使用

const stack = new Stack();
stack.push(5)
stack.push(8)
console.log(stack.size())
console.log(stack.pop())
console.log(stack.show())