Expose lastIndex from iterator

[RReverser]

We should probably still expose lastIndex from iterator object itself (as in opposite to old regexp-bound property). This can be useful for some cases like regexp with sticky flag, where we want to know whether our "tokenization" matched entire string or stopped somewhere in the middle as following text didn't match so that we could handle error / try another regexp / whatever.

Otherwise, /^regexp/y for regexpregexpregexp something something regexp and regexpregexpregexp returns same list of matches and it becomes impossible to figure out whether and where the error occured.

[ljharb]

I think exposing it makes sense; how would you suggest exposing lastIndex?

Here are some options that come to mind:

1. set an additional lastIndex property on the match object (normal match objects coming from exec only have input and index, and likely groups after named capture groups land).
2. yield an array of [match, lastIndex]
3. yield an object of { match, lastIndex }

[RReverser]

Hmm I'm now trying to remember whether I simply misunderstood the original proposal (that it returns not just strings but also index) or had something else in mind. If we have index + match.length, it's probably sufficient to figure out if you matched entire string or not.

[ljharb]

Awesome - in that case I'll close this out; but happy to reopen it if there's still something we need to add.