Comprehensive RegExp to remove JavaScript comments

Question

I need to dependably remove all JavaScript comments with a single Regular Expression.

I have searched StackOverflow, and other sites, but none take into account alternating quotes, multi-line comments, comments within strings, regular expressions, etc.

Is there any Regular expressions that can remove the comments from this:

var test = [
    "// Code",
    '// Code',
    "'// Code",
    '"// Code',
    //" Comment",
    //' Comment',
    /* Comment */
    // Comment /* Comment
    /* Comment
     Comment // */ "Code",
    "Code",
    "/* Code */",
    "/* Code",
    "Code */",
    '/* Code */',
    '/* Code',
    'Code */',
    /* Comment
    "Comment",
    Comment */ "Code",
    /Code\/*/,
    "Code */"
]

Here's a jsbin or jsfiddle to test it.

Answer 1

I like challenges :)

Here's my working solution:

/((["'])(?:\\[\s\S]|.)*?\2|\/(?![*\/])(?:\\.|\[(?:\\.|.)\]|.)*?\/)|\/\/.*?$|\/\*[\s\S]*?\*\//gm

Replace that with $1.

Fiddle here: http://jsfiddle.net/LucasTrz/DtGq8/6/

Of course, as it has been pointed out countless times, a proper parser would probably be better, but still...

NB: I used a regex literal in the fiddle insted of a regex string, too much escaping can destroy your brain.

---

Breakdown

((["'])(?:\\[\s\S]|.)*?\2|\/(?![*\/])(?:\\.|\[(?:\\.|.)\]|.)*?\/) <-- the part to keep
|\/\/.*?$                                                         <-- line comments
|\/\*[\s\S]*?\*\/                                                 <-- inline comments

The part to keep

(["'])(?:\\[\s\S]|.)*?\2                   <-- strings
\/(?![*\/])(?:\\.|\[(?:\\.|.)\]|.)*?\/     <-- regex literals

Strings

    ["']              match a quote and capture it
    (?:\\[\s\S]|.)*?  match escaped characters or unescpaed characters, don't capture
    \2                match the same type of quote as the one that opened the string

Regex literals

    \/                          match a forward slash
    (?![*\/])                   ... not followed by a * or / (that would start a comment)
    (?:\\.|\[(?:\\.|.)\]|.)*?   match any sequence of escaped/unescaped text, or a regex character class
    \/                          ... until the closing slash

The part to remove

|\/\/.*?$              <-- line comments
|\/\*[\s\S]*?\*\/      <-- inline comments

Line comments

    \/\/         match two forward slashes
    .*?$         then everything until the end of the line

Inline comments

    \/\*         match /*
    [\s\S]*?     then as few as possible of anything, see note below
    \*\/         match */

I had to use [\s\S] instead of . because unfortunately JavaScript doesn't support the regex s modifier (singleline - this one allows . to match newlines as well)

This regex will work in the following corner cases:

• Regex patterns containing / in character classes: /[/]/
• Escaped newlines in string literals

---

Final boss fight

And just for the fun of it... here's the eye-bleeding hardcore version:

/((["'])(?:\\[\s\S]|.)*?\2|(?:[^\w\s]|^)\s*\/(?![*\/])(?:\\.|\[(?:\\.|.)\]|.)*?\/(?=[gmiy]{0,4}\s*(?![*\/])(?:\W|$)))|\/\/.*?$|\/\*[\s\S]*?\*\//gm

This adds the following twisted edge case (fiddle, regex101):

Code = /* Comment */ /Code regex/g  ; // Comment
Code = Code / Code /* Comment */ /g  ; // Comment    
Code = /Code regex/g /* Comment */  ; // Comment

This is highly heuristical code, you probably shouldn't use it (even less so than the previous regex) and just let that edge case blow.