_JavaScript_stack

stack.js

class Stack{
    constructor() {
        this.list = [];
        this.top = null;
    }

    push(v) {
        this.list.push(v);
        this.top = v;
    }

    pop() {
        if (this.top === null) {
            return null;
        }

        let r = this.list.pop();
        if (!r) {
            this.top = null;
        }
        else {
            this.top = this.list[this.list.length-1];
        }

        return r;
    }

    peek() {
        return this.top;
    }
}

let s = new Stack();
s.push(1)
s.push(2)
s.pop();
s.push(3)
s.pop();
console.log(s.peek()); // 1