如何使用async/await或promise使代码同步运行

Question

当我运行此代码时，首先运行的是content_2函数，而不是content_1。下面的代码异步运行，第二个函数使用第一个函数中的一个变量；node.js存储"要运行，所以我需要content_2在content_1开始运行之前等待它完成，我希望它同步运行。

const content_1 = function main_Content(req, res, callback) {
const assert = require('assert');
const fs = require('fs');
const mongodb = require('mongodb');
const mv = require('mv');
var filename = req.body.Filename + Math.ceil((Math.random() * 1000000000000) + 10);
console.log(req.body.Filename)
//CREATE A FILE 
fs.writeFile(filename + '.html', req.body.Content, (err) => {
if (err) throw err;
console.log('File was created successfully...');
});
//MOVE TO UPLOADS
const currentPath = path.join(__dirname, "../", filename + ".html");
const destinationPath = path.join(__dirname, "../uploads", filename + ".html");
mv(currentPath, destinationPath, function(err) {
if (err) {
throw err
} else {
console.log("Successfully moved the file!");
}
});
const uri = 'mongodb://localhost:27017';
const dbName = 'registration';
const client = new mongodb.MongoClient(uri);
client.connect(function(error) {
assert.ifError(error);
const db = client.db(dbName);
var bucket = new mongodb.GridFSBucket(db);

//UPLOAD FILE TO DB THROUGH STREAMING
fs.createReadStream('./uploads/' + filename + '.html').
pipe(bucket.openUploadStream(filename + ".html")).
on('error', function(error) {
assert.ifError(error);
}).
on('finish', function(res) {
var result = res._id
store.set('id', result);
//process.exit(0);

});
});

}

const content_2 = function metaData(req, res, callback) {
const obj = new ObjectId()
var filename = req.body.Filename + Math.ceil((Math.random() * 1000000000000) + 10);
const slice = require('array-slice')
var id = store.get('id');
console.log(id)
var objID = slice(id, 14, 24)
console.log(objID + '2nd')
Key.findByIdAndUpdate(req.body.id, {$push: {Articles:{Title: req.body.Title, Desc:req.body.Desc, Content: {_id: `ObjectId("${objID}")`}}} }, (err, docs) => {
if(err){
console.log(err)
}else{
console.log('done' + obj)
}
});

}

Answer 1

我将给您举两个例子。第一个是使用承诺。第二个将使用异步等待。不过输出完全相同。

放弃这三种方法。有人打扫房间；那么"；有人检查房间是否干净；那么"；付款完成。

承诺版本

const cleanRoom = new Promise((res, rej) => {
console.log("Cleaning room...");
setTimeout(() => {
console.log("Room clean!");
res();
}, 2000);
});
const cleanCheckup = () => {
return new Promise((res, rej) => {
console.log("Clean checkup...");
setTimeout(() => {
console.log("Checkup complete!");
res();
}, 2000);
});
}
const payMoney = () => {
console.log("Open Wallet!");
return new Promise((res, rej) => {
setTimeout(() => {
res("50€");
}, 2000);
});
}
cleanRoom
.then(cleanCheckup)
.then(payMoney)
.then(console.log);

异步/等待版本

const sleep = mils => {
return new Promise(r => setTimeout(r, mils));
};
const cleanRoomAW = async () => {
console.log("Cleaning room...");
await sleep(2000);
console.log("Room clean!");
};
const cleanCheckupAW = async () => {
console.log("Clean checkup...");
await sleep(2000);
console.log("Checkup complete!");
};
const payMonney = async () => {
console.log("Open Wallet!");
await sleep(2000);
return "50€";
};
async function run() {
await cleanRoomAW();
await cleanCheckupAW();
const value = await payMonney();
console.log(value);
};
run();

请注意helper方法sleep，因为您还不能在浏览器中等待setTimeout。(在nodejs>=16中，我相信您不需要这个helper方法(

您可以将这两个版本中的任何一个复制/粘贴到浏览器的控制台中，并确认两个版本都同步运行，尽管setTimeout具有异步性质。