Creating new model in backbone?

Question

I want to create a new model based on some parameter. JSBin Demo

var M1 = Backbone.Model.extend({
  defaults: { type: 'one', value: 1 }
});

var M2 = Backbone.Model.extend({
  defaults: { type: 'two', value: 2 }
});

var getModel = function(type) {
  var map = { 'one': M1, 'two': M2 };
  return map[type];
};

// Error in this line (Undefined is not a function)
var model = new getModel('two')();

console.log(model.get('value'));

I have tried several notations but could not pin-point the reason.

1. This works fine

var mapModel = {
  'one': M1,
  'two': M2
};

new mapModel['two']();

2. Does not work

var model = new (getModel('two')());
var model = (new getModel('two'))();

I do not understand what is undefiend and why I am seeing this error.

Answer 1

I think it this case is better to update getModel function and delegate it creating model instances.Lets create factory from getModel

var getModel = function(type) {
    var map = { 'one': M1, 'two': M2 };
    return new map[type];
};

Then you can use it to get new instance of proper type model:

var model = getModel('two');