validate user by express-validator - node.js

Question

I am kind of new to the nodeJs and I am trying to check if user's email already exists in the database, but seems like I am doing something wrong, it always tell me that "Email already exists" I tried a few different ways but none of them work. I hope someone here will be able to help me figure this out. thank you.
router.post('/register', function (req, res) {
var name = req.body.name;
var email = req.body.email;
req.checkBody('name', 'Name is required').notEmpty();
req.checkBody('email', 'Email is required').notEmpty();
req.checkBody('email', 'Email already exists').custom(email => {
return User.getUserByEmail(email, function(user) {
if (user) {
throw new Error('this email is already in use');
}
})
});
// User.getUserByEmail(email, function (err, user) {
//
// if(!isEmpty(user)){
// console.log(user);
// MyEmitter.emit('isUser', true);
// var empty = '';
// req.checkBody('empty', 'Username/Email is already taken').isEmpty();
// }
// });
/** CKECK IF USER EXISTS NEEDS TO BE WORKED ON */
var errors = req.validationErrors();
if (errors) {
res.render('register', {
errors: errors
});
}else {
var newUser = new User({
name: name,
email: email,
username: username,
password: password
});
User.createUser(newUser, function (err, user) {
if (err) throw err;
});
req.flash('success_msg', 'Registration successful, please log in');
res.redirect('/users/login');
}
});
/** get user by email **/
module.exports.getUserByEmail = function(email, callback){
var query = {email: email};
User.findOne(query, callback);
}

Answer 1

Check this one:
req.checkBody('email', 'Email already exists').custom(email => {
User.findOne({email: email}).exec(function(user) {
if (!user) {
return true;
}
else{
return false;
}
})
});