Open-source and online code collaboration has created so many great libraries on the net.  Some of the most useful for any web designer is the variety of JavaScript libraries.   They may seem overwhelming at first, but learning and adapting anyone one of them will definitely increase the rate at witch you can code.  A basic JavaScript library will have a host of integrated features, including easy access to the DOM (all the HTML elements in a live web page), event handling, animation and varied Ajax support.

There are  abundance of different libraries available with varied followings. A few examples are:

Jquery

• By far the most popular library. There must a million different mini plugins/extensions available across the web.
• Definitely not the fastest library available.
• Great for adding small features to a website, but I would not recommend it for web applications.

Prototype

• One of the older libraries, but has kind of died off.
• Prototype does not have effects/animation built in, keeping it nice and slim.
• script.aculo.us is the effect/animation add-on for Prototype.

Dojo

• Dojo has a pretty positive following, mainly fueled by its integration with the Zend framework.

Mootools

• Includes a comprehensive library.
• Really fast.
• Has an interesting library builder on the website that allows you to only include the functions you are going to use, reducing the footprint.
• Probably one of the better ones for web application development.
• Unfortunately, the site went down while I wrote this.

EXTJS

• This is a great JavaScript web application library started by one of the main contributors to the YUI project.
• Has a host of great web application widgets (trees, panes, etc.).
• The look is rather restrictive

All and all, learning any one of the libraries will render you familiar with a majority of the others.  A lot of the functionality is very similar, so I’ve included the slides from my Introduction to Prototype seminar.  Feel free to use it as your own.