user_model.js

//The model could be used both server and browser side, 
//not much more than a plain object with some simple getters and setters.
let User = Model.extend({
  first_name: String,
  last_name: String,
  full_name: function(){
    return this.first_name + ' ' + this.last_name;
  }
});

//The repository should be server side only, this handles the db and mapping user updates
let UserRepo = Repository.extend({
  model: User,
  table: 'users'
  //custom queries + extended Repository base methods like findById etc
});


//Server side
let user = UserRepo.findById(1);//returns an instance of User

user.first_name = 'test';

UserRepo.save(user);

//Browser side
//user passed via inline js into window or something like that on load, not really important.
let user = window.user;

user.first_name = 'something';

//no way to directly save user here, you will need some rest api for that BY DESIGN!!!
ApiService.updateUser(user)
  .then(function(response){
    if(response.status == 200 && response.body.status == 'success'){
      //...
    }
  });