> Because CoffeeScript is all well and good but I really don't see how it is useful, except from maybe speeding up your development a little

You have a weird concept of "useful" if "speeding up your development" isn't a part of it :-)

the quote is "maybe speeding up your development a little"

> Do you think by using Opal or RedScript is possible to avoid learning JavaScript?

RedScript essentially supports JS syntax plus Ruby-like syntax, and allows them to be freely mixed, so you probably need to learn JS for RedScript, especially if you ever have to read code that comes from someone else.

Opal is Ruby, but allows inlining JS (using the mechanism regular Ruby uses for inline shell commands, essentially, the JS interpreter is the "system shell") which I suspect is going to be fairly heavily used in Opal projects until there are more Ruby wrappers around JS functions (e.g., DOM-related ones) necessary for even the most basic web work. So, you probably need to know JS to make effective use of Opal for now, though that may not be true forever.

CoffeeScript doesn't have to eliminate JavaScript to be useful. Just having a better notation for passing anonymous functions as parameters makes such a huge difference on code clarity that I think it's worthwhile.

It's amazing how many people on the web aren't interested in making their lives easier.

Try using promises, and a small utility function to convert library functions that take callbacks to ones that return a promise.