How can this regex be made JavaScript compatible?

Question

I have found a regex template in Expresso, this one works fine and returns perfect matches but in JavaScript it doesn't work. I know its may be for look-behind, but I am not enough efficient in Regex to make it JS compatible.

\((?>[^()]+|\((?<number>)|\)(?<-number>))*(?(number)(?!))\)

I want to match it with ...

max(50, max(51, 60)) a() MAX(s,4,455)something

... and it should return ...

1: (50, max(51, 60))

2: ()

3: (s,4,455)

This works perfectly in Expresso but JS console in Chrome says:

Uncaught SyntaxError: Invalid regular expression: /\((?>[^()]+|\((?<number>)|\)(?<-number>))*(?(number)(?!))\)/: Invalid group

How can this regex be modified to function properly in JavaScript?

score 6 · Answer 1 · edited May 23 '17 at 12:22

6

JavaScript does not support named capture groups (?<number>)

As suggested in this question, regex may not be the right tool for the job. However, if you simply want to match the outermost parenthesized groups you can use this

/\([^)]*(\s?\))*\)/g

See it working at http://refiddle.com/114

edited May 23 '17 at 12:22

Community

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1

answered May 04 '11 at 16:07

Paul Alexander

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Thanks Paul, it works in the given string but doesn't return expected result in different string. AVG(ROUND(5,8),10,11)*MAX(MAX(5),10,AVG(5)) Any suggestion? – Muhammad Usman May 04 '11 at 16:39
Yeah, regex doesn't really handle nesting very well. You might be better off writing a tokenizer and parsing the string manually yourself instead of using regex. – Paul Alexander May 04 '11 at 16:48

Gumbo · Accepted Answer · 2011-05-04T16:40:10.027

Assuming that your given regular expression is a .NET regular expression, the following syntax components are not supported by JavaScript:

(?>…) – nonbacktracking subexpression
(?<name>…) – named matched subexpressions
(?<name1-name2>…) – balancing group definition
(?(name)…) – conditional group

To get the same result with JavaScript, you’ll need to do the balancing on your own:

var parts = str.match(/[()]|[^()]+/g),
    matches = [],
    balance = 0;
for (var i=0, j=0; i<parts.length; i++) {
    switch (parts[i]) {
    case "(":
        if (balance === 0) {
            j = i;
        }
        balance++;
        break;
    case ")":
        if (balance === 1) {
            matches.push(parts.slice(j, i+1).join(""));
        }
        balance--;
        if (balance < 0) {
            throw new EvalError('parentheses are not balanced; unexpected "("');
        }
        break;
    }
}
if (balance > 0) {
    throw new EvalError('parentheses are not balanced; missing ")"');
}

Matt Kellogg · Answer 3 · 2011-05-04T16:12:53.293

2

There's no negative lookbehind in Javascript. You'll have to find an alternative.

Edit: I looked at your RegEx again, and I thought I saw negative lookbehind, but I guess I didn't. I'll leave this for informational purposes anyways.

edited May 04 '11 at 16:12

answered May 04 '11 at 16:06

Matt Kellogg

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Check this link for lookbehind in JavaScript: http://blog.stevenlevithan.com/archives/mimic-lookbehind-javascript – Rocket Hazmat May 04 '11 at 16:07
And there's your alternative. Thanks, Rocket. – Matt Kellogg May 04 '11 at 16:08

score 0 · Answer 4 · answered May 04 '11 at 16:07

0

In javascript, numbers can be defined with [0-9] or \d Not a digit is [^0-9] or \D

answered May 04 '11 at 16:07

Plahcinski

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How can this regex be made JavaScript compatible?

4 Answers4