Sergio Pereira & Scott Raymond 
Prototype Quick Reference [PDF ebook] 

This short cut provides a complete quick reference to the Prototype Java Script framework. Prototype is an open-source library that is particularly useful to developers of dynamic Ajax applications, and to other web developers who need to work with DOM elements.If you’re a web developer building sophisticated, user-friendly applications, you should be using Prototype. This reference gives you everything you need to use Prototype to its fullest.This document covers Prototype 1.4. There will be a free upgrade to the Prototype 1.5 version of this document.