I remember reading something about how JavaScript has so many backwards-compatibility edge cases that it's extremely difficult to write a performant engine. Unfortunately I can't find my source.
Lua has the turtle's mindset. It's gone slow and steady, and its releases are anything but frequent. However, that just goes to show how stable of a product it is.
(Considering the context, maybe a turtle wasn't the best comparison...)
Here's JavaScript V8 :: Lua http://shootout.alioth.debian.org/u32/benchmark.php?test=all...