I'm mostly thinking about how many of the problems highlighted in "Javscript: The Good Parts" have been fixed in Lua, while Javascript can't be fixed. Not a matter of design and taste, but outright bugs.
That's what I try to do, which turns it into a crippled Ruby. And there's no getting around it silently doing the wrong thing if I ever forget a "var" or "===".
For what it's worth, there are tools that can help you avoid the bad parts. JSLint won't let you forget a "var" or "===" ... and if you use CoffeeScript, it's not possible to forget "var" or "===", because there aren't any.