Well, you have to keep in mind that this is JS for Acrobat. 99% of the JS reference you'll find online will be geared toward using it in web-pages, which is different. The core JS syntax of both is the same, but Acrobat/Reader JS has its own objects and methods that are not available in the web-based JS, and vice versa.
For generic JS info, see: JavaScript Tutorial
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference
For Acrobat JS info, see: http://www.adobe.com/devnet/acrobat/javascript.html