面试题答案是我自己写的，有不对的地方请评论区指出！！！ღ( ´･ᴗ･` )比心

1.事件循环

async function async1(){
    console.log(1);
    await async2()
    console.log(2);
  }

  async function async2(){
    console.log(3);
  }

  console.log(4);

  async1()

  setTimeout(()=>{
    console.log(5);
  },0)

  new Promise((resolve)=>{
    console.log(6);
    resolve()
  }).then(()=>{
    console.log(7);
  })

  console.log(8);

输出顺序：

2.手写Promise.all源码

3.算法：栈

用例1：输入：["1","3","+","6","*"] 输出：24 计算过程：（1+3）*4=24 用例2：输入：["22","5","-","5","/"] 输出：3 计算过程：（22-5）/4=3

function fn(args) {
    let stack = [], res = 0, num = 0
    for (let i = 0; i < args.length; i++) {
      if (args[i] === "+") {
        num = Number(stack[stack.length - 2]) + Number(stack[stack.length - 1])
        stack.pop()
        stack.pop()
        stack.push(num)
      } else if (args[i] === "-") {
        num = Number(stack[stack.length - 2]) - Number(stack[stack.length - 1])
        stack.pop()
        stack.pop()
        stack.push(num)
      } else if (args[i] === "*") {
        num = Number(stack[stack.length - 2]) * Number(stack[stack.length - 1])
        stack.pop()
        stack.pop()
        stack.push(num)
      } else if (args[i] === "/") {
        num = Math.floor(Number(stack[stack.length - 2]) / Number(stack[stack.length - 1]))
        stack.pop()
        stack.pop()
        stack.push(num)
      } else {
        stack.push(Number(args[i]))
      }
    }

    return stack[0]
  }

  console.log(fn(["1", "3", "+", "6", "*"]));
  // console.log(fn(["22","5","-","5","/"]));

4.react hooks写一个从100减到0的倒计时

//App.jsx
import React,{useState,useEffect} from 'react'

export default function App(props){
  const [timerID, setTimerID] = useState(null);
  const [counter, setCounter] = useState(100);

  useEffect(() => {
    if(counter > 0){
      let timer = setTimeout(() => {
        setCounter(counter-1)
      }, 1000);
      setTimerID(timer)
    }else{
      console.log("时间到！！！");
    }
    
    return () => {
      setTimerID(null)
    }
  },[counter]);
  
  return (
    <div>
      <p>{counter}秒后将计时结束...</p>
    </div>
  );
}