ep9 v8: Initial implementation of optional chaining ⛓️‍💥

Modern Javascript has been steadily evolving, and in 2020 we saw the advent of optional chaining - a small but mighty language feature that found lightning quick adoption.

The syntax is simple - const errorMessage = res.body.error?.message

Once a spec for a language feature is agreed upon, how exactly does it get implemented? For NodeJS, Deno, and modern Chrome-powered browsers, we look to Google’s v8 Javascript engine for a ~250 LoC implementation.

This commit is essentially a quick tour through compiler design - v8’s scanners, tokens, parsers, ASTs, and bytecode generation all get small adjustments to make room for Token::QUESTION_PERIOD.

Links references:

• https://github.com/v8/v8/commit/ceb7bd59432a340ea3711ef5acb8c148471eee8c

• https://v8.dev/blog/scanner

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Optional_chaining

• https://en.wikipedia.org/wiki/Visitor_pattern