Not sure if this should be part of TSTL. There are already JS build systems that incorporate that functionality (e.g. gulp, grunt, make). Even a simple shell or npm script would work fine.

Especially because all the tasks mentioned don't need any information from TSTL and can just be standalone programs/scripts.

optimizing/minifying/obfuscating/bytecode-compilation/etc

@lolleko Pinged you on Discord, see the relevant chat; the purpose of afterEmit is to remove annoyance of having to run npm script manually all the time, in other words, I need a hook which will run after transpiled files have been written to disk to allow third-party tools to work upon those files, and here comes the key part - it also has to be incremental friendly (tstl --watch). I was told by Perry that this should be incremental friendly, hence afterEmit PR.