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I'm trying to find out if a string contains css code with this expression:

var pattern = new RegExp('\s(?[a-zA-Z-]+)\s[:]{1}\s*(?[a-zA-Z0-9\s.#]+)[;]{1}');

But I get "invalid regular expression" error on the line above...

What's wrong with it?

found the regex here:

It's for PHP but it should work in javascript too, right?

I'm trying to find out if a string contains css code with this expression:

var pattern = new RegExp('\s(?[a-zA-Z-]+)\s[:]{1}\s*(?[a-zA-Z0-9\s.#]+)[;]{1}');

But I get "invalid regular expression" error on the line above...

What's wrong with it?

found the regex here: http://www.catswhocode./blog/10-regular-expressions-for-efficient-web-development

It's for PHP but it should work in javascript too, right?

• javascript
• jquery
• css

Share Improve this question Follow asked Jan 29, 2012 at 17:12 AlexAlex 66.2k185185 gold badges460460 silver badges651651 bronze badges 2

• 4 I would suggest avoiding that website. Taking coding advice from a cat is probably a bad idea in general. – Pointy Commented Jan 29, 2012 at 17:32
• 1 While CSS isn't a terribly plex language, it is probably a bit too plex to be detected reliably with a single regex. My guess is that there are better ways to solve this problem. – benekastah Commented Jan 29, 2012 at 17:48

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4 Answers 4

Sorted by: Reset to default 3

What are the ? at the start of the two [a-zA-z-] blocks for? They look wrong to me.

The ? is unfortunately somewhat overload in regexp syntax, it can have three different meanings that I know of, and none of them match what I see in your example.

Also, your \s sequences need the backslash escaping because this is a string - they should look like \\s. To avoid escaping, just use the /.../ syntax instead of new Regexp("...").

That said, even that is insufficient - the regexp still produces an Invalid Group error in Chrome, probably related to the {1} sequences.

The ?'s are messing it up. I'm not sure what they are for.

/\s[a-zA-Z\-]+\s*:\s*[a-zA-Z0-9\s.#]+;/

worked for me (as far as piling. I didn't test to see if it properly detected a CSS string).

Replace the quotes with / (slashes):

var pattern = /\s([a-zA-Z-]+)\s[:]{1}\s*([a-zA-Z0-9\s.#]+)[;]{1}/;

You also don't need the new RegExp() part either, which is why it's been removed; instead of using a quote or double quote to denote a string, JavaScript uses a slash / to denote a regular expression, which isn't a normal string.

That regular expression is very bad and I would avoid its source in the future. That said, I cleaned it up a bit and got the following result:

var pattern = /\s(?:[a-zA-Z-]+)\s*:\s*(?:[^;\n\r]+);/;

this matches something that looks like css, for example:

background-color: red;

Here's the fiddle to prove it, though I'd remend to find a different solution to your problem. This is a very simple regex and it's not save to say that it is reliable.

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