Erm, so you could possibly do some stuff like this (probably not for Js). It's called profile guided optimisation - you compile, run, take measurements, and the

Erm, so you could possibly do some stuff like this (probably not for Js). It's called profile guided optimisation - you compile, run, take measurements, and the compiler uses those measurements to pick the right optimisations to use. I don't know how desirable it would be - you'd be shifting the burden from the compiler to the network, basically. In particular, you'd still have to compile it, which means that all you're gaining is the time before JIT decides that the code's super hot. A nicer approach might be like Oracle hints - you have a small comment you place above a function that tells the JIT how you want it compiled. You test your software using an instrumented browser, and that adds the comments between you finishing and it running. It kinda ups the complexity by loads, though - and I bet the benefits would be relatively small. Stuff like minifying and compressed assets has really tangible benefits, but here you have something that can easily be done wrong, and really only improves the execution of a very small overall percentage of functions.