check if username and email is unique in database - mongodb

Question

Tried searching the net for 2 days and still could not find a specific answer. I have the below node.js code for user routes and models. How can I check if the username and email has never appear in the MongoDB, and prompt the user a message if there is?
model:
var mongoose = require('mongoose');
var bcrypt = require('bcryptjs');
// User Schema
var UserSchema = mongoose.Schema({
username:{type: String , required:true, index: true, unique:true},
email:{type: String, required:true, index: true, unique:true},
password:{type: String, required:true}
});
module.exports = mongoose.model('User', UserSchema)
route:
var express = require('express');
var router = express.Router();
var User = require('../models/user');
var bcrypt = require('bcryptjs');
// Get Homepage
router.get('/', function(req, res){
res.render('index');
});
router.get('/register',function(req,res){
res.render('register');
});
// submit form
router.post('/submit', function(req, res){
// retrieve data from posted HTML form
var username = req.body.username;
var email = req.body.email;
var password = req.body.password;
var password_confirm = req.body.password_confirm;
// express validator
req.checkBody('username','Username is required').notEmpty();
req.checkBody('email','Email is required').notEmpty();
req.checkBody('email','Invalid email').isEmail();
req.checkBody('password','Password is required').notEmpty();
req.checkBody('password','Password must contain at least 6 characters').isLength({min:6});
req.checkBody('password_confirm','Password mismatch').equals(req.body.password);
// store the errors
var errors = req.validationErrors();
if(errors){res.render('register',{errors:errors});}
else {
// hash password
var salt = bcrypt.genSaltSync(10);
var hash = bcrypt.hashSync(password, salt);
password=hash;
// load data into model
var newUser = new User ({username:username, email:email, password:password});
// save the new user
newUser.save(function(err,newUser){
if(err){console.error(err);}
// console.error is same, but in stderr form
else{
console.log('new user saved successfully');
console.log(newUser);
}
});
res.redirect('/');
}
});
module.exports = router;

Answer 1

app.post('/authenticate', function(req, res) {
var user = new User({
username: req.body.username
});
user.save(function(err) {
if (err) {
if (err.name === 'MongoError' && err.code === 11000) {
// Duplicate username
return res.status(500).send({ succes: false, message: 'User already exist!' });
}
// Some other error
return res.status(500).send(err);
}
res.json({
success: true
});
});
})
You have to catch the error and return it to the front end of your application. This code above should demonstrate how to achieve this by using server status 500. Regarding searching the web, this answer and question are quite similar to this previous question:
How to catch the error when inserting a MongoDB document which
violates an unique index?
I hope this helped to some extend.