Now in PDF as a Beta Book from Pragmatic Programmers with a dead tree version coming later this year: Prototype and script.aculo.us by Prototype core team member, script.aculo.us contributor and Google Group help wizard Christophe Porteneuve.
Basically, with this book in your arsenal, you’ll quickly make the transition from just using Prototype to being the resident code ninja.
Needless to say, the book is completely up-to-date (and also covers features from the yet-to-be-released version 1.5.2 of Prototype!), to help you stay on top of things.
Of course, not only does Christophe show you how to really leverage Prototype, but there’s a second beta on the way, providing the same coverage for script.aculo.us, which I really look forward too!Tweet