My new job will take me much further into JavaScript than I have gone in the past, even though I am not the JavaScript guy. I mentioned some time ago that JavaScript is underestimated, but I still have not learned (much less internalized) all of those lessons.

Alex Russell gives some fundamental principles of JavaScript (which he erroneously calls idioms) which would go a long way toward modernizing my approach to the language.

These days there are many powerful JavaScript libraries available. They are great either as a toolkit to use in web apps, or as advanced textbooks in how JavaScript can be used. Here’s a sampling:

• prototype provides an AJAX framework and lots of other JavaScript utilities. It is often used as a foundation by other libraries in this list.
• Behaviour lets you add JavaScript handlers to elements using CSS syntax rather than onClick attributes.
• script.aculo.us provides lots of cool functionality like visual effects, autocompletion, and drag and drop.
• Rico provides AJAX, visual effects, and drag and drop.
• Dojo is a large library providing many features, enough that it is available in different subsets (“Editions”). Included are AJAX, visual effects, and rich text editing.
• jQuery provides CSS and XPath selectors for accessing elements, among other tools.

For a more complete list, check out Saddam Azad’s JavaScript libraries roundup.

Finally, if you aren’t quite ready to take on a whole library but want to get started using cooler functions, or at least understanding what all the excitement is about, Dustin Diaz has a list of the top 10 custom JavaScript functions of all time.