minifies like typescript compilers, etc can remove dead code. I recall some minifiers that definitely did - whether they're still in use I don't know (I haven'

minifies like typescript compilers, etc can remove dead code. I recall some minifiers that definitely did - whether they're still in use I don't know (I haven't been working in engine dev for a few years). For JSC's parsing the most expensive things are strict mode, and certain "errors" which basically trigger a rollback in the parser and then a reparse with more validation.