Question

Let’s say I wanted to have this API for an example to do app:

var db = new Database('db-name'); // DB connection
var todo = new Todo(db); // New "Todo" and pass it the DB ref
// I want this API:
todo.model.create('do this', function (data) {
  console.log(data);
});

I have it setup currently like:

function Todo (storage) {
  this.storage = storage;
};

Todo.prototype.model = {
  create: function (task, callback) {
    // The problem is "this" is Todo.model
    // I want the "super", or Todo so I can do:
    this.storage.save(task, callback);
  }
}

So, if you see the comment, the problem is that “this” inside of model.create is obviously referencing Todo.model, but I need it to grab the “super“.

Best I could think of was:

Todo.prototype.model = function () {
  var self = this;
  return {
    create: function (task, callback) {
      // The problem is "this" is Todo.model
      // I want the "super", or Todo so I can do:
      self.storage.save(task, callback);
    }
  }
}

But both of these aren’t great. The biggest problem is that I don’t want to have all my methods on model inside of a single object (1st example) or function (2nd). I want to be able to take them out from inside of the model def. Secondly, I’d like to have the todo.model.create API.

Is there a design pattern to achieve this?

Answer 1

You can’t use the prototype pattern for todo.model as you’ve written it because model is a property of todo.

I think you need:

1. a new Model object, on which you can use the prototype model.

2. in the Todo constructor, create a Model object. Ideally, use a read-only “getter” function to allow that model object to be accessed, but not overwritten.