javascript - JavaScript 中 Async Await 中的关键字 "await"是否仅适用于 Promise？

Question

当 await 写入异步函数时，例如 -

let x = await doSomething()

doSomething 函数必须返回 Promise 吗？

Answer 1

它可能会返回任何内容，因为

let x = await doSomething()
// ... rest of your code

// is roughly equivalent

Promise
  .resolve(doSomething())
  .then(value => {
    let x = value

    // ... rest of your code
  })

但是如果 doSomething 是异步的，它必须返回一些“thenable”的东西，这样 await 才能真正工作

const doSomething = () => ({
  then(fn) {
    setTimeout(fn, 2000, 'hello')
  }
})

const run = async () => {
  let msg = await doSomething()
  
  console.log(msg)
}

run().then(() => console.log('Done'))