How to make callback function in Coffeescript

Question

I can't find out how to make a function that calls another function at the end.

I want to be able to do something like this:

book.save (err) ->
  MyFunc param1, param2, (callbackParam) ->
    # some code using callbackParam

MyFunc = (param1, param2) ->
  # some other code that defines callbackParam
  ?.call(callbackParam)

What has to be called and how does it receive the data?

Answer 1

If you want to call MyFunc as:

MyFunc param1, param2, some_function

Then it should look like this:

MyFunc = (param1, param2, callback) ->
    # some code that defines callbackParam
    callback callbackParam

And if you want to make the callback optional:

MyFunc = (param1, param2, callback) ->
    # some code that defines callbackParam
    callback? callbackParam

And if you want to supply a specific @ (AKA this), then you'd use call or apply just like in JavaScript:

MyFunc = (param1, param2, callback) ->
    # some code that defines callbackParam
    callback?.call your_this_object, callbackParam

The (callbackParam) -> ... stuff is just a function literal that acts like any other parameter, there's no special block handling like in Ruby (your tags suggest that Ruby blocks are the source of your confusion).

Answer 2

Here's a cleaner, easier to read and understand example:

some_function = (callback) ->
  param1 = "This is param1"
  param2 = "This is param2"
  callback(param1, param2)

callback = (param1, param2) ->
  console.log(param1)
  console.log(param2)

@tester = ->
  some_function(callback)
  "done"

Now load your website, go to the console, and call the function:

> tester()
  This is param1
  This is param2
< "done"