JavaScript QuickStart

JavaScript is an object-oriented client-end scripting language that lets you build interactions between page content, the state of the browser, and the actions of the reader. It is a programming language that can make your pages feel more dynamic and give feedback to your user.

JavaScript is used in millions of Web pages to improve the design, validate forms, detect browsers, create cookies, and much more.

Java and JavaScript are two completely different languages in both concept and design!
Java (developed by Sun Microsystems) is a powerful and much more complex programming language - in the same category as C and C++.

Here is a very good link to learn more about Javascript.