I know quite a few languages, and I like Javascript. It has a nice mix of functional, procedural, and object oriented aspects. Once upon a time, it was a horrible language to work in (with browser differences making it infinitely worse); but now, I find I like it.

Now, that said, given the choice, I'd choose coffescript. It gives many of the same benefits in a more concise format. It has its warts as well, though, reflecting its desire to stay as close to a concise-javascript as possible.

I feel like coffeescript largely exists because of early mistakes in javascript, like no heredoc and places where they weakened the language to make it more convenient, like this one I just discovered today (with workarounds) http://stackoverflow.com/a/14510952/539149 and js has a ton of problems because it separated Array and Object, but overall I think it's still probably my favorite language right now. I like lua too but it's less pure, so aspects of it remind me of older languages like pascal.

just a note: Lua is basically a very cleaned up version of Javascript. if their APIs were the same you could practically do a literal transcription between them and most programs would run with little alteration. that includes things like object literals (lua tables).

example:

  (function(a, b) { return a * b; })(1) //valid javascript (NaN)
  (function(a, b) return a * b end)(1) //valid lua (runtime error)

I love Lua because of it's reluctance to use symbols (such as braces). It's mostly an aesthetic thing. I think it looks great.