async与await

function test () {
  return new Promise(resolve => {
    setTimeout(() => {
      console.log('test')
      resolve()
    }, 1000)
  })
}
function test1 () {
  return new Promise(resolve => {
    setTimeout(() => {
      console.log('test1')
      resolve()
    }, 1000)
  })
}
function test2 () {
  return new Promise(resolve => {
    setTimeout(() => {
      console.log('test2')
      resolve()
    }, 1000)
  })
}
async function call () {
  await test()
  await test1()
  await test2()
}
call ()

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继发执行

function call () {
  Promise.all([test(), test1(), test2()])
}
call()

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function getUserInfo (id) {
  return new Promise(resolve => {
    setTimeout(() => {
      resolve({
        id: id,
        name: 'xxx',
        age: 'xxx'
      })
    }, 200)
  })
}
const users = [{id: 1}, {id: 2}, {id: 3}]
let userInfos = []
users.forEach(async user => {
  let info = await getUserInfo(user.id)
  userInfos.push(info)
})
console.log(userInfos) // []

function getUserInfo (id) {
  return new Promise(resolve => {
    setTimeout(() => {
      resolve({
        id: id,
        name: 'xxx',
        age: 'xxx'
      })
    }, 200)
  })
}
const users = [{id: 1}, {id: 2}, {id: 3}]
let userInfos = []
async function call() {
  for (user of users) {
    let info = await getUserInfo(user.id)
    userInfos.push(info)
  }
  console.log(userInfos)
}
call()

继发式的

function getUserInfo (id) {
  return new Promise(resolve => {
    setTimeout(() => {
      resolve({
        id: id,
        name: 'xxx',
        age: 'xxx'
      })
    }, 200)
  })
}
const users = [{id: 1}, {id: 2}, {id: 3}]
let userInfos = []
const promises = users.map(user => getUserInfo(user.id))
Promise.all(promises).then(res => {
  userInfos = res
  console.log(userInfos)
})

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