题解 | 【模板】栈

class Stack {
    constructor(item) {
        this.item = item;
        this.arr = [];
    }

    push(item) {
        this.arr.push(item);
    }

    pop() {
        return this.arr.length === 0 ? 'error' : this.arr.pop();
    }

    top() {
        return this.arr.length === 0 ? 'error' : this.arr[this.arr.length-1];
    }
}

const readline = require('readline');
const stack = new Stack();
const rl = readline.createInterface({
    input: process.stdin,
    output: process.stdout
});
rl.on('line', function (line) {
    const ops = line.split(' ');
    const command = ops[0];
    const arg = ops[1];

    if (typeof stack[command] === 'function') {
        const res = stack[command](arg);
        if (res !== null && res !== undefined) {
            console.log(res);
        }
    } 
});