8、for-of 异步循环

function muti(num){
  return new Promise((resolve,reject)=>{
    setTimeout(()=>{
      resolve(num*num)
    },1000)
  })
var arr =[2,3,4]
// for - of
(async ()=>{
  for(let value of arr){
    const res = await muti(value)
    console.log(res)
  }
})
// forEach
arr.forEach(async item=>{
  const res = await muti(item)
  console.log(res)
})