Recently I have been doing quite a lot of development in JavaScript and I have taken a look at a couple of JavaScript frameworks mainly focusing onthe Dojo toolkit and Prototype. Both of these have their strengths and weaknesses, I must point out one of the biggest strengths of Dojo is, in my opinion, the Dojo.require() method which allows dynamic inclusion of those files/packages required for a given script.

Currently the biggest weakness of both of these is locating documentation, I started by just exploring the source and trying to figure out what functionality they provided.
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Earlier today I came across a few links which are definitely worth a read if you’re looking at Prototype:

Overview of the Prototype Javascript Library
A good quick over of all the functions available in the current public release, ideal as a reference sheet.
Quick Guide to Prototype
A quick introduction to the basic concepts of Prototype and some of the most useful functions.
Developer Notes for prototype.js
This could be described as the Un-official documentation for Prototype, it is very thorough and covers all classes and functions offered by Prototype.
Script.aculo.us Prototype documentation
Script.aculo.us effects library is built using Prototype, they have an overview of all the functionality along with working examples.

For a look at some of the basic features of Prototype in action you can check out my JSDebug utility, which has a version which takes advantage of some Prototype functionality.