Javascript RegEx: Matching indented comments

Question

I am currently trying to parse out comments in a particular format using JavaScript. While I have a basic understanding of regular expressions, with this one I seem to have reached my current limit. This is what I am trying to do:

The comments

//
    This is a
    multiline comment

Code here


//
    This is another
    comment

Again, code here

For the Regex, it currently looks this like this:

\/\/\n(\s+[\s\S]+)

\/\/\n matches the //sequence including the new line.
Since I am interested in the comments, I am opening a capture group.
\s+ matches the indentation. I could probably be a bit more precise by only accepting tabs or spaces in a particular count – for me this is not relevant
[\s\S] is supposed to match the actual words and and spaces between the words.

This seems to currently match the whole file, which is not what I want. What I now can't wrap my head around is how to solve this?

I think my problem is related to me not knowing how to think about regexes. Is it like a program that matches line per line, so I need to work more on the quantifiers? Or is there maybe a way to stop at lines only consisting of a newline? When I try to match for the newline character, I of course receive matches at each line ending, which is not helpful.

Wiktor Stribiżew · Accepted Answer · 2020-05-24 13:06:33Z

1

You may use

/^\/\/((?:\r?\n[^\S\r\n].*)*)/gm

See the regex demo

Details

^ - start of a line (due to m modifier, ^ also matches line start positions)
\/\/ - a // string
((?:\r?\n[^\S\r\n].*)*) - Capturing group 1: zero or more repetitions of
- \r?\n - a CRLF or LF line ending
- [^\S\r\n] - any whitespace but CR and LF
- .* - the rest of the line.

JS demo:

var text = "//\n    This is a\n    multiline comment\n\nCode here\n\n\n//\n    This is another\n    comment\n\nAgain, code here";
var regex = /^\/\/((?:\r?\n[^\S\r\n].*)*)/gm, m, results=[];
while (m = regex.exec(text)) {
  results.push(m[1].trim());
}
console.log(results);

answered May 24, 2020 at 13:06

Wiktor Stribiżew

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1 Comment

Sven Over a year ago

Thank you! With your answer I was able to understand RegExes A LOT better than before. It's like magic once you get the hang of it!

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