Is there any way to not return something using CoffeeScript?

Question

It seems like CoffeeScript automatically returns the last item in a scope. Can I avoid this functionality?

Answer 1

You have to explicitly return nothing, or to leave an expression evaluating to undefined at the bottom of your function:

fun = ->
    doSomething()
    return

Or:

fun = ->
    doSomething()
    undefined

This is what the doc recommends, when using comprehensions:

Be careful that you're not accidentally returning the results of the comprehension in these cases, by adding a meaningful return value — like true — or null, to the bottom of your function.

---

You could, however, write a wrapper like this:

voidFun = (fun) ->
    ->
        fun(arguments...)
        return

(Notice the splat operator here (...))

And use it like this when defining functions:

fun = voidFun ->
    doSomething()
    doSomethingElse()

Or like this:

fun = voidFun(->
    doSomething()
    doSomethingElse()
)

Answer 2

Yes , with a return as the last line of a function.

For example,

answer = () ->
  42

extrovert = (question) -> 
  answer()

introvert = (question) ->
  x = answer()
  # contemplate about the answer x
  return 

If you'd like to see what js the coffee compiles to, try http://bit.ly/1enKdRl. (I've used coffeescript redux for my example)

Answer 3

It seems functions in CoffeeScript must always return something, even null. In C, you have void as a return type. ->, the empty function, compiles to (function() {}), so it's the only function that doesn't return anything.

Answer 4

longRunningFunctionWithNullReturn = ->
  longRunningFunction()
  null

Answer 5

Just something fun(ctional)

suppressed = _.compose Function.prototype, -> 'do your stuff'

Function.prototype itself is a function that always return nothing. You can use compose to pipe your return value into this blackhole and the composed function will never return anything.