Question

I’m trying to figure out the right way to declare a model for a Backbone Collection in CoffeeScript. Let me demonstrate with an example:

class MyApp.Collections.Likes extends Backbone.Collection
  constructor: (@models, @options) ->
  model: MyApp.Models.Like

When I initialize this collection and create a new model, it fails.

likes = new MyApp.Collections.Likes
like = new likes.model // same result for likes.model.new

TypeError: Result of expression 'likes.model' [undefined] is not an object.

Looking at the compiled JavaScript, the model is defined as follows:

MyApp.Collections.Likes = (function() {
  __extends(Likes, Backbone.Collection);
  function Likes(models, options) {
    this.models = models;
    this.options = options;
  }
  Likes.prototype.model = MyApp.Models.Like; // <--
  return Likes;
})();

I could define the model in two ways that will work:

---

Solution 1

class MyApp.Collections.Likes extends Backbone.Collection
  constructor: (@models, @options) ->
  model: -> MyApp.Models.Like // Notice the ->

Which compiles it to:

MyApp.Collections.Likes = (function() {
  __extends(Likes, Backbone.Collection);
  function Likes(models, options) {
    this.models = models;
    this.options = options;
  }
  Likes.prototype.model = function() { // <-- added to the prototype as a function
    return MyApp.Models.Like;
  }
  return Likes;
})();

Solution 2

class MyApp.Collections.Likes extends Backbone.Collection
  constructor: (@models, @options) ->
  @model: MyApp.Models.Like // Notice the @

Which compiles it to:

MyApp.Collections.Likes = (function() {
  __extends(Likes, Backbone.Collection);
  function Likes(models, options) {
    this.models = models;
    this.options = options;
  }
  Likes.model = function() { // <-- not added to prototype
    return MyApp.Models.Like;
  }
  return Likes;
})();

---

I’m pretty sure Solution 1 is the better solution. However, lots of sites I’ve looked at with tutorials define it without the -> or @.

Am I doing something blatantly wrong?

There isn’t anything wrong with the Like model, it’s pretty vanilla:

class MyApp.Models.Like extends Backbone.Model

Answer 1

I’m unable to replicate your error. Here’s my code:

class Like extends Backbone.Model

class Likes extends Backbone.Collection
    model: Like

likes = new Likes
like = new likes.model
console.log like instanceof Like  # true

Is it possible that you made a typo somewhere? In particular, is MyApp.Models.Like defined at the point where you write model: MyApp.Models.Like? The tests

console.log MyApp.Collections.Likes::model?

and

console.log MyApp.Collections.Likes::model is MyApp.Models.Like

should both give you true. And if they do, then new likes.model should be equivalent to new MyApp.Models.Like.