UnhandledPromiseRejectionWarning: Unhandled promise rejection in nodejs server - node.js

Question

I am trying to use postman for the first time and yes i am a beginner with this authentication. I have a register page and a login page in angular and my backend is running on another port which is coded in nodejs. So i have installed passport and other required packages for the login authentication and registering user process. But on sending request to register route for registering a user i get the UnhandledPromiseRejectionWarning error. Even though there is then and catch inside the route it is still giving this error because of which i am confused. The data that i am sending is perfect but the error is occuring on the server side.
Here is my app.js file that contains all the routes
var express = require('express');
var mongoose = require('mongoose');
var bodyparser = require('body-parser');
var cors = require('cors');
var session = require('cookie-session');
var flash = require('connect-flash');
var passport = require('passport');
var bcrypt = require('bcryptjs');
require('./config/passport')(passport);
var User = require('./models/User');
var app = express();
app.use(bodyparser.json());
app.use(cors());
var expiryDate = new Date(Date.now() + 60 * 60 * 1000) // 1 hour
app.use(session({
name: 'session',
keys: ['key1', 'key2'],
cookie: {
secure: true,
httpOnly: true,
domain: 'example.com',
path: 'foo/bar',
expires: expiryDate
}
}))
app.set('port', process.env.port || 3000);
app.use(passport.initialize());
app.use(passport.session());
// Connect flash
app.use(flash());
// Global variables
app.use(function(req, res, next) {
res.locals.success_msg = req.flash('success_msg');
res.locals.error_msg = req.flash('error_msg');
res.locals.error = req.flash('error');
next();
});
var db = mongoose.connect("mongodb://localhost:27017/server", {
useNewUrlParser: true
}, function(err, response) {
if (err) {
console.log('There is error in connecting with mongodb');
}
console.log('Connection has been established.');
});
app.get('/', (req, res) => {
res.send("hello");
});
//Trying registering with passport
app.post('/register', (req, res) => {
console.log(req.body);
debugger;
const { firstname, lastname, email, password } = req.body;
let errors = [];
if (errors.length > 0) {
res.render('register', {
errors,
name,
email,
password,
password2
});
} else {
User.findOne({ email: email }).then(user => {
if (user) {
errors.push({ msg: 'Email already exists' });
res.render('register', {
errors,
firstname,
lastname,
email,
password
});
} else {
const newUser = new User({
firstname,
lastname,
email,
password
});
bcrypt.genSalt(10, (err, salt) => {
bcrypt.hash(newUser.password, salt, (err, hash) => {
if (err) throw err;
newUser.password = hash;
newUser
.save()
.then(user => {
req.flash(
'success_msg',
'You are now registered and can log in'
);
res.redirect('/login');
})
.catch(err => console.log(err));
});
});
}
});
}
});
//end
app.post('/login', (req, res, next) => {
console.log(req.body);
passport.authenticate('local', {
successRedirect: '/dashboard',
failureRedirect: '/login',
failureFlash: true
})(req, res, next);
});
app.listen(app.get('port'), function(err, response) {
console.log("Server is running");
});
passport.js file in config folder
const LocalStrategy = require('passport-local').Strategy;
const mongoose = require('mongoose');
const bcrypt = require('bcryptjs');
// Load User model
const User = require('../models/User');
module.exports = function(passport) {
passport.use(
new LocalStrategy({ emailField: 'email' }, (email, password, done) => {
// Match user
User.findOne({
email: email
}).then(user => {
if (!user) {
return done(null, false, { message: 'That email is not registered' });
}
// Match password
bcrypt.compare(password, user.password, (err, isMatch) => {
if (err) throw err;
if (isMatch) {
return done(null, user);
} else {
return done(null, false, { message: 'Password incorrect' });
}
});
});
})
);
passport.serializeUser(function(user, done) {
done(null, user.id);
});
passport.deserializeUser(function(id, done) {
User.findById(id, function(err, user) {
done(err, user);
});
});
};

Answer 1

To resolve this specific issue, you need to provide a catch() when you execute User.findOne() at the same level as the outermost then():
User.findOne({ email: email })
.then(user => { /* existing code */})
.catch(err => console.log(err)); // add catch()
And:
// Match user
User.findOne({ email: email })
.then(user => { /* existing code */ })
.catch(err => console.log(err)); // add catch()
Regarding the issue with the engine. You need to specify a rendering engine such as pug or html or ejs, this is something that Express as a framework expects. The link you provided that you are basing this code off of is using a rendering engine, specifically ejs. This is evident from the use of res.render(), which renders templates from the "views" folder.
app.set('view engine', 'ejs');
Even with the rendering engine, set you don't actually need to render any templates. As long as you remove res.render() and instead just use res.send() or equivalent, you can use this Express application as an API.
If your intention is to NOT use templates but still render the built angular files, you need to update the code and remove all instances of res.render() and res.redirect(). You can instead, still setting a view engine to satisfy Express, do something along the following:
// towards top of file
app.use(express.static(path.join(__dirname, 'path/to/built/angular')));
// ...
// after all other routes
app.get('*', (req, res) =>{
res.sendFile(path.join(__dirname+'/path/to/built/angular/index.html'));
});
Hopefully that helps!