It's a good question ( I have a YouTube video on some of the reasonings, https://www.youtube.com/watch?v=8qm49TyMUPI ) but the TLDR is that TS really wants to only be a type layer above JS - turning into something like MSIL means breaking JS runtime semantics or re-creating that in MSIL ourselves. The idea has been tried a little differently by MS research though, https://www.microsoft.com/en-us/research/publication/static-...