I'm building a MEAN app.

This is my Username schema, the username should be unique.

var mongoose = require('mongoose');

var Schema = mongoose.Schema;



module.exports = mongoose.model('User', new Schema({ 

    username: { type: String, unique: true }

}));

On my post route I save the user like this:

app.post('/authenticate', function(req, res) {

        var user = new User({

            username: req.body.username

        });



        user.save(function(err) {

            if (err) throw err;



            res.json({

                success: true

            });



        });

    })

If I post with the same username again I get this error:

MongoError: insertDocument :: caused by :: 11000 E11000 duplicate key
error index:

Can someone explain how instead of the error to send a json like { succes: false, message: 'User already exist!' }

Note: After I post the user I will automatically authentificate, dont need password or something else.