Coffeescript array.sort(a,b) generates failing JS

Question

I am working with coffeescript (version 1.11.1) and I ran into something that I'm struggling to describe. I was simply trying to sort an array of objects by a field, which I can do like so:

data.sort (a,b) ->
    if a.name < b.name then -1 else if a.name > b.name then 1 else 0

This produces the following javascript:

data.sort(function(a, b) {
  if (a.name < b.name) {
    return -1;
  } else if (a.name > b.name) {
    return 1;
  } else {
    return 0;
  }
});

Awesome. But in my first attempt I did this instead:

data.sort(a,b) ->
    if a.name < b.name then -1 else if a.name > b.name then 1 else 0

And the generated javascript is for that is:

data.sort(a, b)(function() {
  if (a.name < b.name) {
    return -1;
  } else if (a.name > b.name) {
    return 1;
  } else {
    return 0;
  }
});

Which, because javascript is so helpful, fails silently (at least in Chrome) and causes the surrounding function to return prematurely. A little frustrating but I'll get over it.

First I want to confirm that is expected behavior. I think it probably is and I have some vague thoughts bouncing around my skull about why it does this but I was hoping to get a firmer understanding. How should this be described or what terminology is relevant for this feature of the language?

Answer 1

That is the expected behaviour.

---

CoffeeScript supports all of the following:

• (a, b) -> 5 notation for functions,

• -> 5 notation for functions without arguments,

• f(a, b) notation for function calls, and

• f a notation for function calls (implicit parentheses).

So how do you call the result of a function call f(a, b) with a function parameter -> 5?

The answer is—

f(a, b) -> 5

—which as you've noticed, looks rather similar to—

f (a, b) -> 5

—which translates to calling f, passing the function (a, b) -> 5 as a parameter.