Perhaps the best way to write a transpiler so there's no bugs is to write two of them at the same time, i.e. in this case Lua-to-JS and JS-to-Lua. Maybe it's easier to catch bugs.

This mirrors the idea of writing a compiler for a new language in itself as soon as possible.

Get a Clue: http://cluecc.sourceforge.net/

Decent timing from LuaJIT1 when it was generating "dirty" Lua bytecode.