How to find indices of groups in JavaScript regular expressions match?

Question

When I write a regular expression like:

var m = /(s+).*?(l)[^l]*?(o+)/.exec(\"this is hello to you\");
console.log(m);

I get a match object

Answer 1

You can't directly get the index of a match group. What you have to do is first put every character in a match group, even the ones you don't care about:

var m= /(s+)(.*?)(l)([^l]*?)(o+)/.exec('this is hello to you');

Now you've got the whole match in parts:

['s is hello', 's', ' is hel', 'l', '', 'o']

So you can add up the lengths of the strings before your group to get the offset from the match index to the group index:

function indexOfGroup(match, n) {
    var ix= match.index;
    for (var i= 1; i