JavaScript RegExp - Match HTML Tag Containing Line Breaks

Posted on 2007-12-07
Last Modified: 2008-02-07
I need a regular expression that matches HTML tags which can contain line breaks / carriage returns. This is easy in Perl or PHP because the dot (any) token matches line breaks, but unfortunately it does not in JavaScript. The attached code demonstrates the problem Change the regular expression to make it match the <p> tag and it's contents to win the prize.
		<title>Regular Expression Test</title>
		<script language="javascript" type="text/javascript">
			var s;
			s += "<html>\n";
			s += "	<body>\n";
			s += "		<p>\n";
			s += "			Match this paragraph\n";
			s += "			even though it contains\n";
			s += "			line breaks\n";
			s += "		</p>\n";
			s += "	</body>\n";
			s += "</html>";
			var re = new RegExp('<p[^>]*>(.*)</p>', 'gim');
			var matches = s.match(re);
			if (matches && matches.length) {
				for (var x = 0; x < matches.length; x++) {
					document.write('<h3>Match found:</h3><xmp>' + matches[x] + '</xmp>');
			} else {
				document.write('<h3>No matches found!</h3>');

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Question by:wwarby
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LVL 11

Expert Comment

ID: 20426624

Not sure what exactly you need here... but putting the \n (newline) regex will match the beginning of the paragraph.



LVL 27

Expert Comment

ID: 20426998
Instead of ".*" in your pattern I would recommend you use "[\S\s]*?"
Note that the use of "?" is required to stop at the first enclosing "</p>" in case you have multiple "<p></p>" blocks in your HTML source.

Author Comment

ID: 20427246
Guys, thanks for your efforts so far but I'm afraid neither of these suggestions has worked in this particular example. Using the source code I provided, I substituted the following regular expressions:

<p[^>]*>(.*)\n</p> (from saleek)
<p[^>]*>([\S\s]*?)</p> (from ddrudik)

...but neither of them match the paragraph tag, at least not in the SpiderMonkey JS engine in Firefox 2.

The example I've given is just a simplification the real problem I'm working on which is a script that strips XML tags from text objects in a proprietary format in our web content management system. I have RegexBuddy and the expression I started with works fine until you emulate JavaScript because the dot can't cross line breaks. I've tried a lot of variations and so far drawn a blank.

I'm pretty desperate to get this script working so if I'm increasing the points to 500. Can I suggest saving the code snippet as an HTML file and testing in a browser - if you get the right regular expression in there it will write the matched code back to the screen.


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LVL 27

Accepted Solution

ddrudik earned 500 total points
ID: 20427421
var re = /<p[^>]*>([\S\s]*?)<\/p>/ig;

Note that you have a group () that you could also reference along with the match, if that's not required then you can remove () above.

Author Comment

ID: 20427620

Thank you very much - that's exactly what I was after. The group () in there since because where I will be using this expression is in a script that strips tags - I need to capture the content of the tags and remove the tags themselves. Where I was going wrong is using the RegExp object constructor rather than the inline constructor you have used. I tried the exact same regular expression constructed both ways - your one works, mine doesn't. I'll be accepting your solution with full marks either way, but I'd be very grateful for your thoughts on why one of these statements works when the other doesn't:

var re = /<p[^>]*>([\S\s]*?)<\/p>/ig;
var re = new RegExp('<p[^>]*>([\S\s]*?)<\/p>', 'ig');


LVL 27

Expert Comment

ID: 20427691
It seems that \'s need to be escaped with \ as:
var re = new RegExp('<p[^>]*>([\\S\\s]*?)<\\/p>', 'ig');

Author Comment

ID: 20428615
Of course ;) I've hit that problem before - should have noticed it.

Thanks very much for this :)
LVL 27

Expert Comment

ID: 20428738
Thanks for the question and the points.

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