If you absolutely need to make heavy use lua on the browser side:
http://kripken.github.io/lua.vm.js/lua.vm.js.htmlAs v8 is an advanced javascript engine that should run faster than one would expect.
If you only need to interact with lua interpreter already running in your core application, or make eventual use of it on the web side, my suggestion is that you make thin v8 (javascript) bindings that passes data between js and lua. This data can eventually be lua source or bytecode, if your lua interpreter implements eval() (it´s on by default but some people don´t even compile it for code size and/or security reasons).
Care must be taken for multi-threading issues and object life cycle as both js and lua has different semantics (and runs garbage collectors so you must keep references now and then).