Groovy or Scala

I'm down to my last choice! Groovy or Scala. I a, a java developer, and I want to learn one of them. I have a few questions on Grails first:

1. Does Grails have some sort of JavaScript interaction? I hear Play! is integrated with CoffeeScript. 

2. Can Grails be used with just Groovy, or can I use Java as well?

That's it for my Grails questions. I seem to know more Groovy, but if there is no JavaScript interaction, I'll use Scala. Both languages have nice Eclipse plugins. So which should I use. I'm open to criticize and praise for each language as well as personal experience.
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