How to get response from nodejs server - node.js

Question

In my application I want to get response from nodejs server. if I enter already registered mail id I want to get "User already exists" message on browser console.log in register.component.ts. How do it?
Many times tried but not able to findout. Please anyone help.
user.js://server
users.post('/register', (req, res) => {
const today = new Date()
const userData = {
first_name: req.body.first_name,
last_name: req.body.last_name,
email: req.body.email,
password: req.body.password,
created: today
}
User.findOne({
email: req.body.email
})
//TODO bcrypt
.then(user => {
if (!user) {
User.create(userData)
.then(user => {
const payload = {
_id: user._id,
first_name: user.first_name,
last_name: user.last_name,
email: user.email
}
let token = jwt.sign(payload, process.env.SECRET_KEY, {
expiresIn: 1440
})
res.json({ token: token })
})
.catch(err => {
res.send('error: ' + err)
})
} else {
res.json({ error: 'User already exists' })
}
})
.catch(err => {
res.send('error: ' + err)
})
})
authentication.service.ts:
public register(user: TokenPayload): Observable<any> {
const base = this.http.post(`/users/register`, user)
const request = base.pipe(
map((data: TokenResponse) => {
if (data.token) {
this.saveToken(data.token)
}
return data;
})
)
return request;
}
register.component.ts:
register() {
this.auth.register(this.credentials).subscribe(
() => {
this.router.navigateByUrl('/profile')
},
err => {
console.error(err); // how to get error message like "User already exits"
}
)
}