How to use callback in .then() function in Nodejs?

Question

I have nodejs module to fetch data from mongodb database using mongodb driver. Callback is passed to given function which return a promise, but instead of returning result in.then() function, it is passing value to callback function. How can I call this function from other module or function since it is not returning it in.then()? I tried to console the result of.then(), but it is showing undefined.

 const MongoClient = require('mongodb').MongoClient; const Db = require('../model/db'); Db.findUser = (details, callback) => { return dbconnection().then(db => { if (db) { return db.collection('users').findOne({ email: details.email, pass: details.password }).then(data => { if (data) { console.log('Found one'); callback(true); } else { let err = new Error(); callback(err); } }) }

I have used following function to call the promise. I am new to promises.

 var getUser = function(callback) { db.findUser().then(result => { console.log(result) // undefined }) }

Answer 1

You can easily do it using async/await . Something like this:

Db.findUser = async (details, callback) => {
  const db = await dbconnection();
  const data = await db.collection('users').findOne({
    email: details.email,
    pass: details.password
  });

  if (data) {
    console.log('Found one');
    callback(true);
  } else {
    let err = new Error();
    callback(err);
  }

  return data;
}

and consume it like:

const getUser = async (details, callback) => {
  const data = await Db.findUser();

  // do whatever you need with data  

  return data;  
}