Extend Coffeescript subclass function from parent in marionette

Question

I've got a "FormView" class in my Marionette application that sets up a lot of things for form submissions around my app. I use it every time there is a form. I've also got some helpers that I want to pass into every form template via the templateHelpers method, but I also want to be able to add additional templateHelpers in the children. Like so:

class Views.FormView extends Marionette.ItemView
  templateHelpers: ->
    helpers: Marionette.Concerns.Helpers

class Views.NewUser extends Views.FormView
  templateHelpers: ->
    variable: @something

I want to be able to access both @variable and @helpers from the template for NewUser. Additionally, I know how to handle this (via _.extends) if templateHelpers is an object, but I need it to be a function.

Is it possible? And if so, how?

Answer 1

In Backbone, when you inherit from another class, Backbone will give the subclass a __super__ property (double underscore at both ends) which is the prototype of the parent class. So from within your Views.NewUser class, you can get the prototype via View.NewUser.__super__. Then, you can call templateHelpers on that object. Here's how I did it (live example at JSbin):

Views = {}

class Views.FormView extends Marionette.ItemView
  templateHelpers: ->
    helpers: "Parent Value"
  logHelpers: ->
    console.log @templateHelpers()

class Views.NewUser extends Views.FormView
  templateHelpers: ->
    variable: "Child Value"
  logHelpers: ->
    console.log @templateHelpers()
    console.log Views.NewUser.__super__.templateHelpers()


formView = new Views.FormView()

formView.logHelpers() // { helpers: "Parent Value" }

newUser = new Views.NewUser()

newUser.logHelpers()

// { variable: "Child Value" }, { helpers: "Parent Value" }

You could then use _.extend to extend one with the other; maybe like this:

initialize: ->
    @helpers = _.extend @templateHelpers(),
        Views.NewUser.__super__.templateHelpers()

Answer 2

Assuming that when you say "parent" you mean "parent view" rather than OO ancestor. What you want to achieve can be done by doing the following: 1. Pass the data object from parent to child view using the itemViewOptions (or childViewOptions in newer Marionette). It can contain functions. 2. In you child view you can do the following:

templateHelpers: ->
  _.extend super(), @options.someOptionsFromParent