JavaScript

JavaScript

Java is a programing language developed by Sun. Java allows programmers to create programs. One example is Java Applets, a small program embedded within a web page.
JavaScript is a scripting language developed by Netscape and later joined in a partnership with Sun. You can insert it directly to your HTML documents. Creating JavaScript is not difficult. What you need are only simple text editor and browser that supports JavaScript.

JavaScript

We are not going to show you how to write JavaScript here because useful JavaScripts are widely available for you to copy. You may not need to know how to write it unless you want customized Script for your site. If you want to learn how to write the script, try JavaScript for the world wide web book.
Shown below are some examples of useful JavaScripts and links to some JavaScript web sites

Alert message:

If you enter this page from the link on the main page, you will get an alert message. Try it again: Click here
Here is the code for the above message:
Click here

Dynamic images and menus:

Dynamic menu can either be created by JavaScript or JavaApplet. The JavaScript version will work only on Netscape 3.0 or higher. JavaApplet version should work on both Netscape and Explorer but it will run much slower than JavaScript.
JavaScript example:
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The principle is that you have two images. One will be displayed when you put your mouse on it, and the other will be displayed when the mouse is off the image.

For more details : http://www.tips-tricks.com/j_script.asp