Nodejs: Can't get data from the module

Question

Actually, I want to get data and insert into my DB. If it exists, doesn't insert the data. And display the data from DB using the ID.

After Inserting the new data, I have to display the new data.

I'm using Nodejs and MongoDB with a third-party API to fetch data.

Journals.findOne({pubmedId: pubmedID}, function(err, results) {
if (err) {
    console.log(err);
    res.status(500);
} else if (results) {
    res.status(400);
    res.send(results);
    console.log("PudmedID should be unique. Pubmed Data already exists! " + pubmedID);

} else {
    newMedjournalData.save((err, Journals) => {
        if (err) {
            console.log(err);
            res.status(500);
            res.send({
                "error": "Can't Insert the data " + pubmedID
            });
            console.log("Can't Insert the data - " + err + " - " + pubmedID);
        } else {
            res.status(200);
            // res.send({ "success": "Successfully Inserted data " + pubmedID });
            console.log("Successfully Inserted data " + pubmedID);

            var getData = getpubMedData(pubmedID);
            console.log(getData);
            res.send(getData);
        }
    });
   } 
 });

I have created a function - getpubMedData to get data from DB after inserting the data.

But I got undefined from console.log(getData);

I refered a Stackoverflow answer.

And added a module - med_data.

const Journals = require('./models/journals');

var med_data =  function (pubmedID) {
        console.log(pubmedID);
        Journals.findOne({ pubmedId: pubmedID }, function (err, results) {

                if (err) {
                        console.log(err); 
                        return {"error": err};
                } else if(results){
                        console.log(results);
                        return results;

                }
        });
}

module.exports = med_data;

and added following,

const getpubMedData = require('../med_data');

But here,

var getData = getpubMedData(pubmedID);

console.log(getData);

res.send(getData);

I got again Undefined

If it is a wrong way, Please suggest me the best way. If my logic is wrong, Please help me to fix the issue.

Answer 1

I/O calls happens async in js. You must provide a way to recover data once async code ends. You can do this using callbacks or promises.

For callback do something like:

var med_data =  function (pubmedID, callback) {
        console.log(pubmedID);
        Journals.findOne({ pubmedId: pubmedID }, function (err, results) {

                if (err) {
                        console.log(err); 
                        return {"error": err};
                } else if(results){
                        console.log(results);
                        callback(results);
                }
        });
}

and

// var getData = getpubMedData(pubmedID)
getpubMedData(pubmedID, function(response) {
    console.log(response);
    res.send(response);
});