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?

Answer 1

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 ")"');
}