Although Christian Heilmann covers what he wished he knew about JavaScript earlier, he actually points out the features JavaScript developers should know: shortcut notations, JSON, native JavaScript functions, event delegation, anonymous functions and the module pattern, allowing configuration, and using good libraries to abstract away browser differences.
Tim Huegdon and Mark Aidan Thomas create an elegant wrapper to the YUI Connection Manager that manages repeating Ajax JSON requests. Tim describes the use of Custom Events, and the use of the Observer design pattern, dissects the code and offers a tidy demonstration of the working code. This simplifies JSON requests into declaring a simple function to process the returned JSON object, and a single line to fire off the request (within a setInterval if required)