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.
Andy Hume whittles away the various JavaScript libraries to produce a clear explanation of event delegation and how it works. Its a technique that reduces the number of event listeners attached to the document by attaching just one event listener to a container element. He presents a simple code example and talks about the benefits of event delegation, including performance and code maintenance. (Includes workarounds for IE and a Safari bug)
Tim Huegdon uses JavaScript to fix Safari's bug where clicking on a label doesn't set focus to the corresponding field element (a useful accessibility aid). Using YUI and event delegation Tim walks us through the development of this piece of code involving attaching an event listener, getting the target of an event, then finding the field that corresponds to the label, and focusing on it if its a text field, or activating / selecting the form element if its a radio button or checkbox.