[mikedouglas]

Does it, really? Most of the optimizations mentioned in the article (compression/obfuscation, module system, yslow integration) or in these comments (debugging, refactoring, auto completion) are all available/possible in javascript alone. What tangible benefits require Java's type system?

[mmastrac]

Guided code splitting and type tightening (with associated devirtualization) are serious optimizations that can't be done today in JS. GWT can guarantee the immutability of JS object shapes - something you can't do with bog-standard JS.