First Scripting Language for Web

I want to get off my mind of C and ((Scheme)) for a while and learn a scripting language for the web. My professor asked me if I could do a Javascript job for him and I said, I'd have to learn it first.

I want to learn Javascript or CoffeeScript but since the latter is simply a transcompiler for the other, should I learn Javascript first before getting to Coffeescript? I heard Coffeescript often makes more optimized code than Javascript, what if I just learn Coffeescript and submit the transcompiled code to my professor?

>>1 you have many options if you want to avoid JS:

Emscripten: An LLVM-to-JavaScript Compiler
(obviously is not intended to use with the DOM, but it's useful if you want to avoid Flash or Java applets)
https://github.com/kripken/emscripten/wiki

LiveScript is a language which compiles to JavaScript.
If you are thinking to learn CoffeeScript you should first check this one.
http://livescript.net/

Wisp is homoiconic JS dialect with a clojure syntax, s-expressions and macros.
http://jeditoolkit.com/try-wisp/

Sibilant is a lisp-family language that compiles to readable and idiomatic JavaScript.
http://sibilantjs.info/

LispyScript - A javascript With Lispy Syntax And Macros
(the ``best'' of both worlds?)
http://lispyscript.com/

btw, javascript engines are superfast now (check V8), plus asm.js (http://asmjs.org/) will allow near native performance inside your browser.