Can't set headers after they are sent - express.js - angular 4 - node.js

Question

./models/user.js
var mongoose = require('mongoose');
var validator = require('mongoose-unique-validator');
var Schema = mongoose.Schema;
const schema = new Schema({
firstName:{ type: String, required: true },
lastName: {type: String, required: true},
password: {type: String, required: true},
email: {type: String, required: true, unique: true },
transactions: [{type: Schema.Types.ObjectId, ref: 'Transaction'}]
});
schema.plugin(validator);
module.exports = mongoose.model('User', schema);
app.js
var express = require('express');
var path = require('path');
var favicon = require('serve-favicon');
var logger = require('morgan');
var cookieParser = require('cookie-parser');
var bodyParser = require('body-parser');
var mongoose = require('mongoose');
var appRoutes = require('./routes/app');
var userRoutes= require('./routes/user');
var app = express();
mongoose.connect('localhost:27017/remake');
// view engine setup
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'hbs');
// uncomment after placing your favicon in /public
//app.use(favicon(path.join(__dirname, 'public', 'favicon.ico')));
app.use(logger('dev'));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({extended: false}));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));
app.use(function (req, res, next) {
res.setHeader('Access-Control-Allow-Origin', '*');
res.setHeader('Access-Control-Allow-Headers', 'Origin, X-Requested-With, Content-Type, Accept');
res.setHeader('Access-Control-Allow-Methods', 'POST, GET, PATCH, DELETE, OPTIONS');
next();
});
app.use('/user', userRoutes);
app.use('/', appRoutes);
// catch 404 and forward to error handler
app.use(function (req, res, next) {
return res.render('index');
});
module.exports = app;
'./routes/item.js'
var express = require('express');
var router = express.Router();
const mongoose = require('mongoose');
const User = require('../models/user');
const bcrypt = require('bcryptjs');
router.post('/', function(req, res, next) {
User.findOne({email: req.body.email}, (err, user) => {
if(err){
return res.status(500).json({
title: 'An error has occured',
error: err
});
}
if(user){
return res.status(401).json({
title: 'Email already taken!',
error: {message: 'Email already taken!'}
});
}
});
const user = new User({
firstName: req.body.firstName,
lastName: req.body.lastName,
email : req.body.email,
password: bcrypt.hashSync(req.body.password, 10)
});
user.save( (err, result) => {
if(err){
return res.status(500).json({
title: 'An error has occured',
error: err
});
}
res.status(201).json({
title: 'User created!',
obj: result
});
});
});
module.exports = router;
It's fine every time I create a user - but as soon I create a user with the same email it would throw this error.
> _http_outgoing.js:504
> throw new Error('Can\'t set headers after they are sent.');
> ^
>
> Error: Can't set headers after they are sent.
> at validateHeader (_http_outgoing.js:504:11)
> at ServerResponse.setHeader (_http_outgoing.js:511:3)
> at ServerResponse.header (/Users/sean/Angular/appdev-remake/node_modules/express/lib/response.js:719:10)
> at ServerResponse.send (/Users/sean/Angular/appdev-remake/node_modules/express/lib/response.js:164:12)
> at ServerResponse.json (/Users/sean/Angular/appdev-remake/node_modules/express/lib/response.js:250:15)
> at Query.User.findOne (/Users/sean/Angular/appdev-remake/routes/user.js:16:36)
> at /Users/sean/Angular/appdev-remake/node_modules/kareem/index.js:177:19
> at /Users/sean/Angular/appdev-remake/node_modules/kareem/index.js:109:16
> at _combinedTickCallback (internal/process/next_tick.js:95:7)
> at process._tickCallback (internal/process/next_tick.js:161:9)
I already put return statements for every instance I could find - is this an express/mongo bug or is there something wrong with my code. I've previously coded this REST API and put them side to side, they're literally the same but this one won't work.

Answer 1

Your calling user.save outside of the scope of the callback of User.findOne
See below - I have put the creation of a user inside the User.findOne callback:
router.post('/', function(req, res, next) {
User.findOne({email: req.body.email}, (err, user) => {
if(err){
return res.status(500).json({
title: 'An error has occured',
error: err
});
}
if(user){
return res.status(401).json({
title: 'Email already taken!',
error: {message: 'Email already taken!'}
});
}
//this is inside the callback
const user = new User({
firstName: req.body.firstName,
lastName: req.body.lastName,
email : req.body.email,
password: bcrypt.hashSync(req.body.password, 10)
});
user.save( (err, result) => {
if(err){
return res.status(500).json({
title: 'An error has occured',
error: err
});
}
return res.status(201).json({
title: 'User created!',
obj: result
});
});
});
});
In your code, the return is effectively being called twice, hence the error