题解 | #【模板】栈#

const rl = require("readline").createInterface({ input: process.stdin });
var iter = rl[Symbol.asyncIterator]();
const readline = async () => (await iter.next()).value;

void async function () {
    class Stack {
      #pointer = -1 // 栈顶指针，栈空时为-1
      constructor() {
        this.items = [] // 用js数组存储数据，原始为动态容量
      }

      push(x) {
        this.items[++this.#pointer] = x // 进栈
      }
      pop() {
        if(!this.isEmpty()) {
          return this.items[this.#pointer--] // 出栈
        } else {
          return 'error'
        }
      }
      top() {
        if(!this.isEmpty()) {
          return this.items[this.#pointer] // 取栈顶元素
        } else {
          return 'error'
        }
      }
      isEmpty() {
        return this.#pointer === -1 // 判空
      }
    }
    const stack = new Stack()
    while(line = await readline()){
        const arr = line.split(' ')
        if(arr[0] === 'push') {
          stack.push(arr[1])
        }
        if(arr[0] === 'pop') {
          console.log(stack.pop())
        }
        if(arr[0] === 'top') {
          console.log(stack.top())
        }
    }
}()