Sure, and that's why Asm.JS(regular JS with special semantics) and later Wasm(bytecode translateable to JS) was so brilliant. It already worked on Safari, they had the option of either:

A: look slow compared to other engines that supported it

B: implement it

Now, stuff like the exception handling stuff and tail calls probably aren't shimmable via JS, but at this point they don't gain much from being obstructionists.