How to send an confirmation email after registration nodejs

I want to add the code to send email in this function.
I’ve also installed 2 libraries: jsonwebtoken and nodemailer. I’ve seen some code related to this topic but I’m new to javascript and nodejs and i could not seem to make the code work. I could use some help!
Thanks in advance!
This is my code.

app.post('/insertuser',function(_req,res){
    var data =JSON.parse(_req.body.data);
    var username = data.username;
    var age = data.age;
    var password = data.password;
    var fname = data.fname;
    var lname = data.lname;
    var address = data.address;
    var city = data.city;
    var email = data.email;
    var sq = data.sq;
    var answer = data.answer;
    var pnumber = data.pnumber;
    var dataentered = data.dataentered;

    mysqlConnection.connect(function(){
        var query = "Insert into Customer (Username,Age,Password,First_Name,Last_Name,Email,Address,City,Phone_No,SQ,Answer,Date_Entered) values('"+username+"','"+age+"','"+sha1(password)+"','"+fname+"','"+lname+"','"+email+"','"+address+"','"+city+"','"+pnumber+"','"+sq+"','"+answer+"','"+dataentered+"')";
        mysqlConnection.query (query,function(err,results,_fields){
            if(err)
                {
                    console.log(err);
                    res.send('Please try again!');
                }
            else{
                    if(results.affectedRows>0)
                    {
                        res.send('Thanks for registering! Please confirm your email! We have sent a link!'); 
                        //the code for affirmation

                    }
                    else{
                        res.send('Please try again!');
                    }

                }
        })
    })
}); 

Answer

You can use nodemailer library for sending emails. I will explain how to send emails from a gmail account. First you need to enable Less Secure App Access in your gmail account security section.

After that, create a transporter using nodemailer:

const nodemailer = require('nodemailer');

var transporter = nodemailer.createTransport({
  service: 'gmail',
  auth: {
    user: '[e-mail]',
    pass: 'password'
  }
});

Then in your code, use created transporter to send mails.

mysqlConnection.query (query,function(err,results,_fields){
    if(err) {
        console.log(err);
        res.send('Please try again!');
    } else {
        if(results.affectedRows>0) {
            //the code for affirmation
            var mailOptions = {
                from: '[e-mail]',
                to: '[e-mail]',
                subject: 'Sending Email using Node.js',
                text: 'That was easy!'
            };

            transporter.sendMail(mailOptions, function(error, info) {
                if (error) {
                    console.log(error);
                    //Handle error here
                    res.send('Please try again!');
                } else {
                    console.log('Email sent: ' + info.response);
                    res.send('Thanks for registering! Please confirm your email! We have sent a link!'); 
                }
            });
        } else { 
            res.send('Please try again!');
        }
    }
})

You can refer to nodemailer documentation for more info.