JavaScript RegEx Syntax Error

Question

I have created the following Regular Expression in C# to extract tokens from a string in the format {token}. I developed the regex in C# and confirmed that it works.

// c#
var regex = new Regex(
    "\\{ (?>[^{}]+| \\{ (?<number>) | \\} (?<-number>) )*(?(number)(?!))\\}",
    RegexOptions.IgnoreCase | RegexOptions.CultureInvariant | 
    RegexOptions.IgnorePatternWhitespace | RegexOptions.Compiled);

var matches = regex.Matches("blah {token1} blah blah  blah {token2} blah");

The variable matches ends up containing two matches - "{token1}" and "{token2}".

I need to execute this in JavaScript, but I get a Syntax error in the expression when I try to execute the following line...

// JavaScript
var regex = new RegExp("\\{ (?>[^{}]+| \\{ (?<number>) | \\} (?<-number>) )*(?(number)(?!))\\}");

Is there anything obvious that I am doing wrong?
Am I trying to use RegEx features that are not supported in JavaScript?

morja · Accepted Answer · 2010-12-15 10:21:39Z

4

If you want to match all occurences of "{something}" try:

\{[^\}]*\}

Or is there another condition that has to be met? like {token[0-9]}?

http://rubular.com/ can help with testing.

answered Dec 15, 2010 at 10:21

morja

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1 Comment

Andy McCluggage Over a year ago

No additional requirement. That does actually seem to work for me. The following line gives me the matches I need...text.match(/\{[^\}]*\}/g); It seems I was horribly overcomplicating it. I really struggle with the regex stuff. I have huge respect for anyone who has got their heads round it. Many thanks.

Linus Kleen · Accepted Answer · 2010-12-15 10:19:13Z

4

Independent subexpressions qualified with (?> ... ) aren't supported in Javascript regular expressions. The ? is actually evaluated as a quantifier.

answered Dec 15, 2010 at 10:19

Linus Kleen

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3 Comments

sjngm Over a year ago

This is browser-specific, some actually recognize a more or less extended kind of regular expression.

Andy McCluggage Over a year ago

I figured it would be something like this. Thanks for the info. It sounds like it's back to the drawingboard.

Linus Kleen Over a year ago

Yes. Suppressing capturing using (?: ... ) does work for example.

sjngm · Accepted Answer · 2010-12-15 10:25:27Z

2

The main point is that if you use C# (or Java) you use a string to write the regular expression. In such a string you need to escape all escaping characters again, which is why you need "\\{" to escape a "{". JavaScript however supports its own syntax of regular expression similar to Perl and PHP I think.

answered Dec 15, 2010 at 10:25

sjngm

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1 Comment

Andy McCluggage Over a year ago

So there is more than one problem with this. Incorrectly escaping characters as well as using regex features that the engine doesn't support. I'm good!

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