node.js - 在 Node 中使用 async await 排队作业

Question

我有以下代码。我试图 console.log下一个story仅在前一个story之后已打印，但正在打印Promise { <pending> } .我是 async 的新手和 await .我在这里缺少什么？

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

1. 不要同时使用async function和return promise.. async functions return a promise automatically return the end value, but in this case since you如果正在使用 setTimeout，那么您需要返回一个 promise ，因此只需使用 return promise。

2. forEach 不会等待 promise 完成，所以它会启动所有 promise 然后跳到下一行，因此请改用 for(let e of a){}

3. 您必须 await promise ，例如 let result = await time.promiseTime(ele) 才能实际获取值，否则您只会获取 promise (或者使用 .then(result=>{...}))

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();