Question

(I know my question’s confusing, so see below for example/explanation)

I am trying to match a bunch of things in one big regex and then figure out which subexpression I matched. The problem is when one of my subexpressions has a “collection/sequence” in it, that throws off the index of the subexpressions.

For example, in the below expression, the check for “foo” would be at index 3:

/(one)|(two)|(foo)/g

But in this one, it’s at index 4 (and yes this is a dumb regex, but the example fits):

/(one)|(([tT][wW])?o)|(foo)/g

If you used the below code to try and find “foo”, you’d get something like:

var str = "Some string that only matches foo";

while ( match = reg.exec( str ) )
{
    for ( var i = 1; i < match.length; i++ )
    {
        //Should be 3 but it's not
        if( match[ i ] !== undefined ) break;
    }

    //This won't match foo, because it's now the wrong index
    alert( match[ i ] );
}

How can I do a “one or more” type expression inside a subexpression parentheses without affecting the indexes returned to “match” via “regex.exec”?

(NOTE: don’t hesitate to tell me if this is in any way unclear and I’ll try to come up with a better example and full example code)

Answer 1

(pattern) matches and captures the match. If you want to match, but not capture, use (?:pattern)