前端 promise 笔试题，有大佬解答下吗？

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let resolvePromise = new Promise(resolve => {
  let resolvedPromise = Promise.resolve()
  resolve(resolvedPromise)
})
resolvePromise.then(() => {
  console.log('resolvePromise resolved')
})
let resolvePromiseThen = Promise.resolve().then(res => {
  console.log('promise1')
})
resolvePromiseThen.then(() => {
  console.log('promise2')
}).then(() => {
  console.log('promise3')
})

输出是 promise1 promise2 resolvePromise resolved promise3

大佬们求解释

2 replies • 2021-05-31 09:53:45 +08:00

he1a2s0

May 31, 2021

以 https://www.promisejs.org/implementing/ 的实现为例，promise 内部使用 setTimeout(function,0)来调用后续操作，所以基本上可按嵌套关系和顺序来用 setTimeout 替换一下，整段代码使用 setTimeout 来描述应该是：

```typescript
setTimeout(()=> {
setTimeout(()=>{
console.log('resolvePromise resolved')
},0)
},0)

setTimeout(()=>{
console.log('promise1')
},0)

setTimeout(()=>{
console.log('promise2')

setTimeout(()=>{
console.log('promise3')
},0)
})
```
运行下来会得到同样的输出

he1a2s0

May 31, 2021

不知道回复怎么发代码。。格式乱了