async await

• async函数返回的都是promise对象，不是promise的会自动封装成promise对象

• await前的代码同步执行，await后的代码异步执行

// await 前的代码同步执行，await 后的代码异步执行
async function test(){
  console.log(1)
  await 2
  console.log(2)
}

const p = test()
console.log(p)

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• promise.then，即成功情况，对应await
• promise.catch，即异常情况，对应try...catch

async function test1(){
  return 1
}
async function test2(){
  return Promise.resolve(2)
}
const p1 = test1()
const p2 = test2()

console.log('p1:',p1)
console.log('p2:',p2)

async function test3(){
  const p3 = Promise.resolve(3)
  p3.then(data=>{
    console.log('data-p3-then:',data)
  })
  const data = await p3
  console.log('data-p3-await:',data)
}
test3()

async function test4(){
  const data4 = await 4  //相当于 const data4 = await Promise.resovle(4)
  console.log('data4:',data4)
}
test4()

async function test5(){
  const data5 = await test1()
  console.log('data5:',data5)
}
test5()

async function test6(){
  const p6 = Promise.reject(6)
  try{
    const data6 = await p6
    console.log('data6:',data6)
  }catch(e){
    console.log('err:',e)
    }
}
test6()

image.png