asdf.py

class MyClass:
  def __init__(one, two, three):
    self.one = one
    self.two = two
    self.three = three
  
  @classmethod
  def my_factory_method(one, two, three=None):
    if three is None:
      return MyClassWithoutThree(one, two)
    return MyClass(one, two, three)

howiwoulddoit.js

// option 1
var ParentView = AmpersandView.extend({
  createSubViews: function(opts, views) {
    var context = {};
    this.wwwToggleView = views.get('wwwToggleView', context);
  }
});
  
// option 2
var ParentView = AmpersandView.extend({
  createSubViews: function(opts) {
    var context = {};
    this.wwwToggleView = WWWToggleView.for(context);
  }
});