When defining classes in CoffeeScript, instance methods will execute on the current this context. For normally instantiated objects, this refers to the object itself.

If the instance method is instead passed as a function callback, this represents the object that is executing the callback.

For example, consider the following code:

class Person
  constructor: (@firstName, @lastName) ->

  displayFullName: ->
    console.log "#{@firstName} #{@lastName}"

person = new Person('Tracy', 'Ouellette')
person.displayFullName()

If you run this code, person.displayFullName() will give the following output:

Tracy Ouellette

However, consider what would happen if you used person.deplayFullName() as a callback:

func = (callback) ->
  callback()

func(person.displayFullName)

Its output would be:

undefined undefined

What's going on here...