Question

I would like to nest a number of functions inside a class property as shown below.
Unfortunately, they won’t get access to the main scope of the class.

Can I solve this without passing each nested function a reference to this?

class myClass

  constructor: -> @errors = []

  doSomething: -> @errors.push "I work as expected"

  functions:
    doStuff: ->
      @errors.push "I cant access @errors" # => TypeError: Cannot call method 'push' of undefined

    ugly: (context) ->
      context.errors.push "It works, but I am ugly" # Works fine but requires scope injection

Non-working alternative using suggested fat arrow:

class myClass
  constructor: ->
    @errors = []

    @functions:
      doStuff: =>
        @errors.push "I wont work either" # TypeError: Cannot call method 'toString' of undefined

Optional alternative, which doesn’t write to the global this.errors property:

class myClass

  constructor: ->

    @functions =
      errors: []
      doStuff: ->
        @errors.push "I will write to functions.errors only"

Answer 1

In JavaScript (as the result, CoffeeScript too), methods use this of the object that contains method.

method()                  // this == globalObject
object.method()           // this == object
Math.random()             // this == Math

This usually works well, unless you deal with example like yours:

object.functions.method() // this == object.functions

When dealing with JavaScript, I would avoid having namespace for functions – it doesn’t play well, even with workarounds. For example, you could try putting reference to this object in object.functions, so any function in object.functions would have access to it.

class MyClass
  constructor: ->
    @errors = []
    @functions.self = this

  doSomething: ->
    @errors.push "I work as expected"

  functions:
    alsoDoSomething: ->
      @self.errors.push "Also works!"

This appears to work at first, but could be confusing when you are using properties like apply or call on it, obj1.functions.alsoDoSomething.call(obj2) won’t work as the obj2 is not correct object (user should do obj2.functions instead which can be confusing).

The real solution is: don’t. JavaScript isn’t intended for abuse like this. All object methods should be directly in object prototype. If you have object in it, all methods of it aren’t methods of your object.