webveuje/考试/原题/es6/promise.md

#promise

## 填空
下面的打印结果是什么
```
const promise = new Promise((resolve, reject) => {
  console.log(1)
  resolve()
  console.log(2)
})
promise.then(() => {
  console.log(3)
})
console.log(4)

```
答案  1 2 4 3


下面打印结果是什么

```
const promise = new Promise((resolve, reject) => {
  //resolve('success1')
 
  resolve('success2')
  reject('error)
})

promise
  .then((res) => {
    console.log('then: ', res)
  })
  .catch((err) => {
    console.log('catch: ', err)
  })

```
答案 then: success1

下面打印结果是什么

```

Promise.resolve(1)
  .then((res) => {
    console.log(res)
    return 2
  })
  .catch((err) => {
    return 3
  })
  .then((res) => {
    console.log(res)
  })

```

答案 1 2

下面打印结果是

```

let a = 1;
const promise = new Promise((resolve, reject) => {
  setTimeout(() => {
    console.log('once')
    console.log(a)
    resolve(a++)
  }, 1000)
})

const start = Date.now()
promise.then((res) => {
  console.log(res)
})
promise.then((res) => {
  console.log(res)
})

```
答案
    once
    1
    1

下面代码打印结果是

```
async function asyncFn() {
    return 'hello world';
}
console.log(asyncFn())

```
答案：
    Promise {<resolved>: "hello world"}


下面代码打印结果是
```

async function asyncFn() {
   	return 1;
}
asyncFn()
.then(res => {
    console.log(res);
})

```
答案 1

下面写法是否正确

```
let a = new Promise((res)=>{
	console.log(1)
	res(1)
})
function name(){
	let a = await a;
}

```
答案 错误