Javascript is failz! It is usually very buggy and some people turn it off. However, java script is really simple and can run on like any web hosting site. If you want something more powerful such as php you need to run your own server generally. PHP is good though. I use lots of java.
Javascript is what gives us the ability to implement web 2.0 features. If I really wanted to learn something useful, and maybe wanted to make some extra cash on the side, I'd learn php and javascript. Remember, we're talking about web development here.
/-gC