~~~ //database/init.js const MongoClient = require('mongodb').MongoClient; var url = 'mongodb://localhost:27017/'; exports.MongoDB=()=> { return new Promise((resolve, reject) => { MongoClient.connect(url, { useNewUrlParser: true }, (err, client) => { if (err) throw err; var test = client.db('test'); test.collection('douban').aggregate([{ $lookup: { from: 'detail', localField: 'name_id', foreignField: 'detail_id', as: 'details' } }]).toArray((err, result) => { if (err) throw err; resolve(result) client.close() }) }) }) } ~~~ ~~~ //server.js const {MongoDB} = require('./database/init.js'); const koa = require('koa'); const app = new koa(); (async()=>{ var data = await MongoDB() app.use(async ctx=>{ ctx.body = data; }) console.log(data); })(); app.listen(8080) ~~~