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Remove HTML Comments with PHP

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When it comes to sending content to users, I'm of the belief that less is more.  There's no reason for HTML comments to be sent down to the user -- they simply bloat the payload.  I remove unwanted HTML comments within my WordPress theme, so I thought I'd share the regex that does it:

// Remove unwanted HTML comments
function remove_html_comments($content = '') {
	return preg_replace('/<!--(.|\s)*?-->/', '', $content);
}

That handy function, paired with output buffering, allows me to remove HTML comments from anywhere within the page.  Less load, less cruft for mobile users!

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Discussion

  1. MaxArt

    That would strip out all the comment-like sequences in Javascript code.
    A very rare case indeed, and mixing HTML and Javascript is usually deprecated, but still…
    A fully-fledged HTML-Javascript parser just to prevent this is hardly the effort here.

    Just remember that for backward compatibility for older browsers, script tags’ content are often enclosed in a comment. That would remove the entire script.

    • MaxArt

      I’d like to add that I usually used the sequence [\s\S] instead of the (capturing) group (.|\s). I think it’s faster.

    • You can also do (?:.|\s) to make a group non-capturing. [\s\S] (whitespace or no whitespace) is nonsensical, you could just as well do . (any character).

      David: Why do you do .|\s? As far as I know, . captures all characters, including whitespace.

    • I’ll check it out Fred!

  2. When does this code run?

    The best use I could see for this is a build step, eg you take the template files and them through this on deploy. It feels like a waste of cpu cycles to run something like this per-request?

  3. I like this concept but where/when would you call the function for normal php pages? thx

  4. This is great.

    For my use, I’d prefer this being done from an htaccess file – is this possible at all?

  5. (v)

    what about MSIE conditional comments? ;-)

    my code is like:

    ...
    return preg_replace('/<!--(?!\s*(?:\[if [^\]]+]|))(?:(?!-->).)*-->/s', '', $content);

    • Awesome point, love this — I’ll check it out and if it works I’ll update my post!

    • I tried this but it didn’t work :/ No comments were stripped at all.

    • Hi David, (V), the following mix of your snippets workes for me

      $data = preg_replace(‘//’, ”, $data);

  6. It depends on our framework, it should have a pipeline to minimize the html before sending it into client :D
    But thanks for your useful snippet :)

  7. Wouldn’t this alter IE conditional comments?

  8. Hi David, (V), the following mix of your snippets workes for me

    $data = preg_replace(‘//’, ”, $data);

    2nd try, I used pre but the code was removed …

  9. Hi David, (V), the following mix of your snippets workes for me

    http://pastebin.com/bfzWVFUi

    3rd try, I used pre but the code was removed … please delete my two previous comments

  10. Mike Smith

    I added this code to my functions.php file, however, visitors can still post strong html tags and images on my blog :(

  11. good concept and thanks for that

  12. spongeBob

    Nice approach. But it would be more believable if I you also removed html comments on this page. :) But I liked the regex.

  13. Jack

    Why even bother with putting in HTML comments at all? Since commenting is supposed to be for future developers eyes who will be reading the actual code I just comment in php and then don’t have to worry about comments passed into html.

  14. Full strip function

    function html2txt($document){
    $search = array('@]*?>.*?@si',  // Strip out javascript
                   '@<[\/\!]*?[^]*?>@si',            // Strip out HTML tags
                   '@]*?>.*?@siU',    // Strip style tags properly
                   '@@'         // Strip multi-line comments including CDATA
    );
    $text = preg_replace($search, '', $document);
    return $text;
    } 
    

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