I've tried to get V8 at least to implement smarter TDZ elision for a long time, which would eliminate the need for these shenanigans.

There are some relatively simple heuristics where you can tell without escape analysis that a variable will not be referenced before initialization.

The obviously bad constructions are references in the same scope that happen before the declaration. It'd be nice if these were an early errors, but alas, so keep the TDZ check. The next is any closed over reference that happens before the initializer. These may run before the initializer, so keep the TDZ check. Then you have hoisted closures even if they're after the initializer (eg, var and function keyword declarations). These might run before the initializer too.

But everything else that comes after the initializer: access in the same or nested scope and access in closures in non-hoisted declarations, can't possibly run before the initializer and doesn't need the TDZ check.

I believe this check is cheap enough to run during parsing. The reason for not pursuing it was that there wasn't a benchmark that showed TDZ checks were a problem. But TypeScript showed they were!