Here is another cool REPL Javascript Learn-to-Code site http://www.crunchzilla.com/code-monster
It's targeted for Kids, but I would say it's for all ages groups that want to learn (or improve) coding.
My view is that 'Coding is the new Maths' and is an key still to have.
I really like Code Academy and I can't recommend it high enough!
(btw, the reason why this post doesn't have screenshots is explained here: Idea for improving blog creation productivity (post by screenshot) )