javascript - promise 解决顺序并等待

Question

我有这段代码:

af = async () => {
    Promise.resolve()
    .then(x => console.log("first then"))
    .then(x => console.log("second then"))
    await Promise.resolve()
    console.log("after await")
}

af()

Google Chrome 版本 61.0.3163.91(正式版)(64 位) 当我从 <script> 运行它时，我得到了以下结果:

first then 
after await
second then

但是当我将代码复制/粘贴到控制台并运行它时，我得到了:

first then
second then
after await

node.js 8.5.0 的行为类似。

什么是正确的顺序，为什么会有差异？

//编辑

另一个有趣的是 firefox 55.0.2(64 位) 对于这段代码:

af = async () => {
    Promise.resolve()
    .then(x => console.log("first then"))
    .then(x => console.log("second then"))
    .then(x => console.log("third then"))
    .then(x => console.log("forth then"))
    await Promise.resolve()
    console.log("after await")
}

af()

日志:

first then
second then
third then
after await
forth then

Answer 1

正确的做法是在 Promise.resolve() 之前添加一个 await 来执行“first then”和“second then”控制台日志。这样它将等待完成该 promise ，然后再转到控制台日志以进行“等待后”

这就是您的本意。

af = async () => {
    await Promise.resolve() // NOTE: I added a "await" before the Promise.resolve()
    .then(x => console.log("first then"))
    .then(x => console.log("second then"))
    await Promise.resolve()
    console.log("after await")
}

af()