user.save() does not save (does nothing) in mongodb - node.js

Question

I'm trying to save a user in MongoDB, but it doesn't seem to work. I have no idea why. All i can tell you is that, the code is running and going in the .pre save function but it doesn't enter in the save function promise.
Can you tell me why it is not saving in base ?
Front submit function
handleSubmit(user){
console.log(user);
axios.post('http://localhost:3000/signup', user)
.then(data => {
console.log(data);
console.log("OBVIOUSLY I DON'T SEE THIS LOG EITHER");
}
);
}
app.js (node.js file)
app.post('/signup', urlencodedParser, function(req, res){
let user = new User(req.body);
user.save().then(() => {
console.log("I DON'T SEE THIS LOG");
});
res.end();
});
user.js (node.js file)
UserSchema.pre("save", (next) => {
console.log(this);
console.log("I SEE THIS LOG");
next();
});
const User = mongoose.model('user', UserSchema);
module.exports = User;

Answer 1

maybe a stupid question, but isn't your User in app.js undefined ?
maybe console.log the req.body. because i do not think you are making a user to begin with.
another tip :
use mongoose's create function instead, you will find a example under construction documents:
https://mongoosejs.com/docs/models.html

Answer 2

instead of .then() on your app.js try using a callback.
user.save(function(err, res){
if (err){throw err;}
console.log('test me', res)
})

Answer 3

You are closing your request before the user being saved.
move the res.end() into then function to solve the problem.
Or you can make an async function(req, res) and put await before user.save(), remove then and wait for database to response, like below:
app.post('/signup', urlencodedParser, async function(req, res) {
let user = new User(req.body);
await user.save();
res.end();
});