How to connect mongodb Replicaset in node.js

I have tried this:

const mongoClient = require('mongodb').MongoClient;

const url = 'mongodb://localhost:4000,localhost:4001/bookstore?replicaSet=myapp';


mongoClient.connect(url,(err,db)=>{
    if(err){
        return;
    }
    console.log('connected to the database');
})

But how to export the database object(db)? The db object can be get only in the callback. Could you please give me some advice?

via laoqiren