Backbone.Model => Uncaught TypeError: Object [Object object] has not method 'apply'

I found the problem. I had been going through my code and "optimizing" (so I thought) some of the redundancies.

Instead of this:

define(["backbone"], function( Backbone ){
  var model = Backbone.Model.extend({
        myfunc : function(){ /*do stuff */}
  });

   return model;
});

I had changed a bunch of code to look like this:

define(["backbone"], function( Backbone ){
     return Backbone.Model.extend({
          myfunc : function(){ /*do stuff*/ }
     });
});

Not a problem right? Mostly.

I was ALSO using a nifty trick I read about on another post about getting singleton functionality from require.js modules by returning an instantiated model! Cool... mostly.

I had this:

define(["backbone"], function( Backbone ){
    var singleton = Backbone.Model.extend({
         myfunc : function(){ /*do singleton stuff*/ }
    });

    // because require.js only runs this code once, this essentially creates a singleton!
    return new singleton();
});

and it worked great!

Then I got cocky...

define(["backbone"], function( Backbone ){
    return new Backbone.Model.extend({
         myfunc : function(){ /*do singleton stuff... no more!*/ }
    })();
});

and I started getting my has no method 'apply' error.

It took me the better part of 2 days and lots of frustration to track down the problem and I finally got the answer from this post:

new Backbone.Model() vs Backbone.Model.extend()

It explains nicely how you can instantiate Backbone.Model but Backbone.Model.extend merely provides you with a constructor that you can THEN use to instantiate a custom Backbone.Model object.

I hope this saves someone the pain I just went through.