If you want to build an Internet app, you can use some type of plug in. But you can also use an extension library. This has the advantage that you don't have to install anything. The browser already knows how to process JavaScript.The library I hear the most about is jQuery. However there are a whole lot more. Developers sometimes think that ExtJS does not get enough press.
If you are not integrating it into a commercial product, you can get ExtJS for free. You add some lines of code to your header section to bring in the ExtJS functionality. Then you use the extension library framework.
Some things you might gain from an extension library are drag and drop functionality, help with AJAX, widgets, and event handling. I plan on investigating at least one of these extension libs right after I finish learning JavaScript.
