JavaScript regex \G + offset equivalent

Question

Is there an equivalent of \G in JavaScript regular expressions? I need to match a pattern at an exact offset. Setting the g flag and .lastIndex searches forward from the given index, but won't match at the offset exactly.

XRegExp has this y modifier which might be what I'm looking for, but it doesn't appear to work in Node/V8.

Answer 1

I think the only thing you can do is set .lastIndex to your starting point, try a match with .exec(), and then if you get a match check the updated value of .lastIndex. If it's equal to your starting position plus the length of the match result, then the match began exactly where you wanted.

So:

var re = /banana/g;
re.lastIndex = 6;

var mr = re.exec("hello banana");
if (mr[0].length + 6 === re.lastIndex)
  alert("good banana");

I would never claim that this is a "good" way of doing things, it's just the only possibility I know of.