First, your code snippet is wrong: you need a space before your first paren.

In coffeescript you can do any of the following, or a few other variants:

  doSomething ->
      stuff
    , onerror

  doSomething(->
      stuff
    , onerror
  )

  doSomething (->
      stuff
    ), onerror

  doSomething(
    ->
      stuff
    onerror
  )

  doSomething (-> stuff), onerror