Get "JavaScript: The Definitive Guide" and look at the API reference, it's split into two sections, one for APIs provided with every JavaScript implemetation, and one for APIs provided by browsers.

Currently there's not much compatibility between server-side JavaScript platforms (beyond the minimal set of APIs provided by the language implementations), something we're trying to solve with CommonJS, but that effort has been inhibited by node.js's sudden rise in popularity and refusal to work with CommonJS...