Typescript usually transpiles to javascript, just without the type information, and this is not done in the browser. If you target old browsers it can add maybe

Typescript usually transpiles to javascript, just without the type information, and this is not done in the browser. If you target old browsers it can add maybe add some overhead like babel does. I don't know about javascript's usual JIT compilers, but LuaJIT's JIT compiler (trace compiler) does a pretty good job of figuring out abstractions.