MEAN Stack app - Can't set headers after they are sent - json

Question

I'm basically trying to create a register page using MEAN and I want to check against the database (Mongo using Mongoose) if the user and email already exists, if one of them is true, send a res.json fail.
And if the username and email are not already in the database, continue to add the user.
I'm getting an error "Can't set headers after they are sent." On the Node console and I'm trying to figure out why.
Once User.getUsername() returns a user in the callback (if the username passed exists in the db), shouldn't it return the json and end the request there? Why is it continuing to the User.adduser() function and trying to set the header there too?
Any help is appreciated, thank you.
router.post('/register', (req, res, next) =>{
let newUser = new User({ // Collect body info
name: req.body.name,
email: req.body.email,
username: req.body.username,
password: req.body.password
});
// Check if username is available
User.getUserByUsername(newUser.username, (err, user) => {
if(err) throw err;
if(user){
return res.json({success: false, msg: 'User already exists'});
// I want to end here if there's a user
}
});
//Continue to add user if getUserByUsername() returns false for user
// Add user
User.addUser(newUser, (err, user) => { // Add user
if(err){
return res.json({success: false, msg: 'Failed to register'});
} else {
return res.json({success: true, msg: 'You have been successfully registered!'});
}
});
});

Answer 1

The logic you have doesn't work for as expected because of how asynchronous methods work. The current logic is do User.getUserByUsername then do User.addUser and if either method calls back, handle it. I'm pretty sure you want, do User.getUserByUsername, wait for it's callback, then call User.addUser if necessary. Here's a crude implementation, you could use promises or define the methods outside of the logic to clean it up. Also, make sure you are calling res.end() at some point in your code.
router.post('/register', (req, res, next) =>{
let newUser = new User({ // Collect body info
name: req.body.name,
email: req.body.email,
username: req.body.username,
password: req.body.password
});
// Check if username is available
User.getUserByUsername(newUser.username, (err, user) => {
if(err) throw err;
if(user){
return res.json({success: false, msg: 'User already exists'});
// I want to end here if there's a user
}else{
//Continue to add user if getUserByUsername() returns false for user
// Add user
User.addUser(newUser, (err, user) => { // Add user
if(err){
return res.json({success: false, msg: 'Failed to register'});
} else {
return res.json({success: true, msg: 'You have been successfully registered!'});
}
});
}
});
});