Question

我有以下代码。我仅在打印前一个console.log之后尝试story下一个story，但是它正在打印Promise { <pending> }。我是async和await的新手。我在这里想念什么？

服务器

const express = require('express')
const async = require("async");
const app = express()
const port = 3000
const time = require('./timeoutFun.js')

const array = [
    {author: 'Bill',
    story: ['This', 'is', 'the', 'first', 'story']},
    {author: 'Frank',
    story: ['Here', 'goes', 'another']},
    {author: 'Tom',
    story: ['Fine', 'another', 'things', 'I', 'wrote']},
    {author: 'Sam',
    story: ['No', 'more', 'writings', 'please']}
]

array.forEach(element => {
    console.log(time.promiseTime(element))
});

app.get('/', (req, res) => res.send('Hello World!'))

app.listen(port, () => console.log(`Example app listening on port ${port}!`))

timeoutFun.js

const time = {
    promiseTime: async function (obj) {
        const randomNum = Math.floor(Math.random() * 5)
        return await new Promise(function (resolve, reject) {
            setTimeout(function () {
                resolve(obj.story.toString() + " " + randomNum);
            }, randomNum * 1000);
        })
    }
}

module.exports = time;

Answer 1

不要一起使用async function和return promise。异步函数自动返回一个Promise只是返回结束值，但是在这种情况下，因为您使用的是setTimeout，那么您将需要返回承诺，因此只需使用返回承诺即可。
forEach不等待承诺完成，因此它将全部启动，然后跳至下一行，因此请使用for(let e of a){}
您必须await这样的承诺，例如let result = await time.promiseTime(ele)才能真正获得价值，否则，您只会得到承诺（或者使用.then(result=>{...})）
< / li>

const time = {
    promiseTime: function (obj) {
        const randomNum = Math.floor(Math.random() * 5)
        return new Promise(function (resolve, reject) {
            setTimeout(function () {
                resolve(obj.story.toString() + " " + randomNum);
            }, randomNum * 1000);
        })
    }
};


const array = [
    {author: 'Bill',
    story: ['This', 'is', 'the', 'first', 'story']},
    {author: 'Frank',
    story: ['Here', 'goes', 'another']},
    {author: 'Tom',
    story: ['Fine', 'another', 'things', 'I', 'wrote']},
    {author: 'Sam',
    story: ['No', 'more', 'writings', 'please']}
];

async function main(){
  for(let ele of array){
      let result = await time.promiseTime(ele);
      console.log(result);
  };
}
main();

在Node中等待异步队列

1 个答案: