JavaScript can be used to spice up your Web page with scrolling banners, pop-up messages, online calculators, and other effects. Some folks' Web browsers can't use JavaScript. Other people turn off JavaScript. If you are using a JavaScript on your page, you should not use it to display crucial information unless you have an alternative way of displaying that information. A classic example is a navigation menu.
Some scripts seem like a good idea at the time, but in practice are just plain annoying.
A classic example of this is online tickers. Return to top 3. There are several JavaScript Web sites that provide a wealth of free scripts you download and use. Most of these sites also include tutorials that'll introduce you to the basics of JavaScripts. JavaScript World's a fair site that includes plenty of fun scripts for you to play around with.