const nodemailer = require('nodemailer');
const smtpTransport = require('nodemailer-smtp-transport');
const xoauth2 = require('xoauth2');
const mailTransport = nodemailer.createTransport(smtpTransport,{
    service: 'Gmail',
    auth:{
            xoauth2: xoauth2.createXOAuth2Generator({
            user:credentials.gmail.user,
            pass:credentials.gmail.password,
        })
    }
});

mailTransport.sendMail({
            from:'"createTops" <info@createTops.com>',
            to:credentials.gmail.user,
            subject:'successful completion of form',
            text:'thank you for signing up enjoy createTops.com'
        }, function(err){
            if(err){
                console.error('unable to send email: '+error);
            };
        });

TypeError: this.transporter.send is not a function
at _processPlugins.err (C:desktopexpressnode_modulesnodemailerlibmailerindex.js:214:34)....