The CoffeeScript emperor has no clothes

Subtitle: when CoffeeScript rock stars run around naked in public

Just because you can do something doesn’t mean you should. Leaving the parentheses out of your CoffeeScript might make your code look a bit more “natural”, but it almost always makes the code less readable and in a many cases, it makes it impossible for the CoffeeScript compiler to understand your intent. It’s more “natural” to go around naked but you shouldn’t. Just like you need to cover your private parts when you go outside, I feel strongly that you should properly cloth your CoffeeScript function/method parameters in parentheses.

In the last few months alone, on StackOverflow, there have a been at least six questions that I have flagged as caused by this issue:

In all of the cases above, there is an idiom that you can’t precisely/clearly express without parentheses around function/method parameters. Often, the coder realizes that it’s ambiguous but “hopes” that the compiler can figure out his intent. He posts a question on StackOverflow once he is able to show that it cannot. In all of these cases, the coder has learned CoffeeScript by looking at a bunch of examples that leave out the parentheses and he doesn’t realize that you can put them in… or he wants to know how the cool-kids express it without them. In each case, the answer is invariably, “Simply add parentheses and it will work as expected.”

If this is confusing the compiler and the new users who want to be CoffeeScript cool-kids, we CoffeeScript bloggers should all make an effort to post all examples with the parentheses left in. I’m going so far as to leave them in all of my code and my collaborators seem to appreciate it. If nobody ever needs to read your code, then feel free to walk around naked in a drug-addled state within the privacy of your own home. But as soon as you step out the door, or want anyone else to read your code…

It’s perfectly fine to leave them out of if-statements, while-loop, etc. We like our female rock starts to show a little cleavage and some folks get turned on by Mick Jagger’s tight leather pants.

Chaining (needed for compiler to understand intent)


Calling a parameter-less method (also necessary)

Function/method calling (even when not chaining, for human clarity)

someFunction(parameterA, parameterB)

…I even favor including them when the last parameter is a callback (although I do cringe every time I see that lonesome closing paren a few lines down so I’m OK with you leaving them out in this case).

someMethodNeedingACallback(parameterA, (err, data) -> console.log(data) )

Functions with no parameters (could live without this, but IMHO, it’s more readable with it)

f = () -> return "hello" # notice how I also like to say "return". That's another clarity choice.

One last argument to try to convince you… Python is the most readable programming language out there. The Python BDFL has come out time and again in favor of readability even at the expense of conciseness. Python used to have a parentheses-less print statement, but Guido feels so strongly that this was a mistake, that he went through the very painful backward-breaking change to require parentheses for print function calls in Python 3.0. I would go so far as to argue that we should remove this “feature” from the CoffeeScript spec but even if we don’t, we should stop using it.

I know… you want to show that you are a CoffeeScript cool-kid. You can write a one-line list comprehension that is like a brilliant guitar solo. But I think it’s cooler for my code to be readable and for the compiler to precisely understand what I intend. The list comprehension guitar solo may be showing off but we expect our cool rock stars to show off. However, it’s uncool (even for rock stars) to be drug-addled running around naked in public. Be the rock star without the drugs… or running around without your function/method calls properly clothed in parentheses.

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5 Responses to The CoffeeScript emperor has no clothes

  1. Pingback: The CoffeeScript emperor has no clothes - when... | Javascript | Syngu

  2. thomas says:

    I just wanted to let you know that you are most likely referring to Bob Dylan, not Dillon. Just thought its kind of an uncool mistake in your rockstar posting .Otherwise I totally agree , though I have only very limited experience with writing coffescript code.

  3. +1 our company’s coding standard – – is also pro-parenthesis, we learn’t the hard the way. Although, our opinion differs on the parentheses for wrapping callbacks – as if we need to chain callbacks, we’ll just bump their lines – the practical benefit of this is the same benefit of being able to do away with curly braces which is lines that just have a brace or parenthesis or whatever and nothing else, generally are just clutter that get in the way. I do like the rock star analogy :)

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