Node.js - Check if user exists - node.js

Question

I'm using NodeJS and passport to let users create an account before they can see results of a quiz they've just taken. My challenge is I need to confirm the username is available before the page refreshes because the user will lose their results if this happens.
Again: I need to verify the username is not taken prior to refreshing.
I think I'm close but it is not working. How would I change my code to handle this challenge?
Currently if the user name is taken it returns an error on trying to create an account and the user ends up on the /failpage as shown below.
app.post('/quiz', usernameToLowerCase, emailToLowerCase, function(req, res) {
User.findOne({
username: req.body.username
}, function(err, user) {
if (err) {
alert(err)
if (user) {
alert('this username is already taken. Please choose another.')
console.log('there was a user');
return false;
}
}
});
var user = new User({
username: req.body.username,
email: req.body.email,
password: req.body.password,
})
user.save(function(err) {
console.log('this is the problem' + ' ' + err)
if (err) {
return res.redirect('/failpage')
}
req.logIn(user, function(err) {
if (err) {
console.log(err);
}
console.log('all looks good')
res.redirect('/results');
});
});
});

Answer 1

Solved it with this if anyone else is trying to do the same thing:
in app.js
app.get('/usercheck', function(req, res) {
User.findOne({username: req.query.username}, function(err, user){
if(err) {
console.log(err);
}
var message;
if(user) {
console.log(user)
message = "user exists";
console.log(message)
} else {
message= "user doesn't exist";
console.log(message)
}
res.json({message: message});
});
});
In js
$('#usercheck').on('change', function() {
$.get('/usercheck?username='+$('#usernameValue').val().toLowerCase(), function(response) {
$('#usernameResponseHidden').text(response.message)
if ($('#usernameResponseHidden').html() === "user exists"){
$('#usernameResponse').text('That username is taken. Please pick another')
}

Answer 2

To solve your problem I think you need to routes. At least a app.get('/quiz') which returns a boolean on if the user exists or not. The section User.findOne can be sent in that route instead. You just need to make a request using ajax when he looses focus of the username field of your form, and display a notification if the name is available or not.