Last two lines each throw compiler errors in CoffeeScript 2

super and extends

Due to a syntax clash with super with accessors, “bare” super (the keyword super without parentheses) no longer compiles to a super call forwarding all arguments.

class B extends A
  foo: -> super
  # Throws a compiler error

Arguments can be forwarded explicitly using splats:

codeFor('breaking_change_super_with_arguments')

Or if you know that the parent function doesn’t require arguments, just call super():

codeFor('breaking_change_super_without_arguments')

CoffeeScript 1.x allowed the extends keyword to set up prototypal inheritance between functions, and super could be used manually prototype-assigned functions:

A = ->
B = ->
B extends A
B.prototype.foo = -> super arguments...
# Last two lines each throw compiler errors in CoffeeScript 2

Due to the switch to ES2015 extends and super, using these keywords for prototypal functions are no longer supported. The above case could be refactored to:

codeFor('breaking_change_super_in_non-class_methods_refactor_with_apply')

or

codeFor('breaking_change_super_in_non-class_methods_refactor_with_class')