How do I comment in CoffeeScript? "/* this */" doesn't work

Question

In what ways can you comment in CoffeeScript?

The documentation say you can use three hash symbols to start and close a comment block:

###
  Comments
  go
  here
###

I've found that I can sometimes use the following two formats

`// backticks allow for straight-JavaScript,
 // but the closing backtick can't be on a comment line (I think?)
`

Are there a simpler way to insert short comments in CoffeeScript?

Do NOT use this style**

Since this is getting a lot of views, I want to emphasize that

/* Comment goes here */

produces a MATH error when the /* is on its own line.

As Trevor pointed out in a comment on the question, this is a regular expression, NOT a comment!

If a `/*...*/` comment "works," it's because the CoffeeScript compiler is interpreting it as a regex. Definitely not recommended! — Trevor Burnham, Oct 16 '11 at 02:59
So I guess there is NO WAY in CoffeeScript to have an intra-statement (between characters) comment? — Pete Alvin, Apr 01 '14 at 15:50
Since I'm limited in formatting comments, I'll post an answer at the bottom. — John Deighan, Jan 19 '23 at 02:43

Michael Durrant · Accepted Answer · 2011-11-29T05:16:21.497

280

Use a single # sign

# like this

One character seems pretty minimal ;)

Also:

###
This block comment (useful for ©-Copyright info) also gets 
passed on to the browsers HTML /* like this! */
###

edited Nov 29 '11 at 05:16

answered Oct 16 '11 at 01:08

Michael Durrant

93,410
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497

4

This is usually how you will want to comment; the triple hash is most often used when you want the comment to fall through to the javascript (copyright messages, usually). – Aaron Dufour Oct 16 '11 at 18:44
5

Ah *sigh*. The official docs use the single # form all through their examples, but never actually mention it in the text explanations, it only talks about the block comments. – Gerry Jun 13 '12 at 19:09
1

Unfortunately no way to have block comments that don't show up in output. – nilskp Dec 29 '14 at 12:51

score 24 · Answer 2 · answered Oct 16 '11 at 01:11

The main way to comment is sh/Perl/Ruby/... style # comments:

# This comment goes to the end of the line
# and it won't appear in the "compiled"
# JavaScript version.

You use the block style ### comments when you want a comment to appear in the JavaScript version:

Sometimes you'd like to pass a block comment through to the generated JavaScript. For example, when you need to embed a licensing header at the top of a file. Block comments, which mirror the syntax for heredocs, are preserved in the generated code.

So if you start with

###
PancakeParser is Public Domain
###

then you'd get this JavaScript comment in the generated JavaScript:

/*
PancakeParser is Public Domain
*/

score 4 · Answer 3 · answered Apr 18 '13 at 17:36

4

Beware of ###! If you use ### to separate sections of code (as I do) it's awfully surprising when that code stops working as a result.

answered Apr 18 '13 at 17:36

Mark Wilden

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15

Do you know why? We have the code working locally but not on the build server with ###. – Azat Oct 28 '13 at 23:12
Unfortunately, I noticed this months ago, and I'm not "in that space" right now to have a look at it. – Mark Wilden Nov 06 '13 at 16:48
10

Because a pair makes a block comment? – Nov 08 '13 at 15:12
3

Would not be so surprising if you used a syntax-highlighting editor, with comments appearing in a different color – Nick Perkins Jun 29 '15 at 15:03
4

Why downvote? It's a valid warning. Really, it's saying don't use a solid line of # as a section separator, or you may occasionally get unbalanced block comment pairs. – Jim Mack Dec 08 '16 at 03:52

score 1 · Answer 4 · answered Jan 19 '23 at 02:46

1

For comments in the middle of a line, try:

if somecond `/* hi */` && some other cond, etc.

The backticks cause CoffeeScript to put the enclosed text into the generated JavaScript as is.

answered Jan 19 '23 at 02:46

John Deighan

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score 0 · Answer 5 · answered Jan 19 '23 at 02:51

Unfortunately, CoffeeScript is inconsistent with whether comments introduced with a single # character make it to the output JavaScript. For example:

# testme.coffee

fName = 'John'
lName = 'Smith'
fullName = "#{fName} #{lName}" # |||| $:
if true #comment
    console.log `/* hi */` 'Hello, World!'

compiles to

// Generated by CoffeeScript 2.7.0
(function() {
  // testme.coffee
  var fName, fullName, lName;

  fName = 'John';

  lName = 'Smith';

  fullName = `${fName} ${lName}`;

  if (true) { //comment
    console.log(/* hi */`Hello, World!`);
  }

}).call(this);

Note the missing comment on the line that assigns to fullName.

How do I comment in CoffeeScript? "/* this */" doesn't work

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