JavaScript is the most widely used scripting language and it is supported by all major browsers. JavaScript is not related to Java in any way. Both are very different languages used for very different purposes. JavaScript became popular because it added interactivity to static HTML pages. This interactivity has been further enhanced since arrival of AJAX on the market. Following are different ways JavaScript makes HTML pages interactive.

- JavaScript allows dynamic text to be placed in HTML pages
- JavaScript can respond to events such as clicking on something
- JavaScript can read and write HTML
- JavaScript can detect browser settings and read and write cookies
- JavaScript can be used to process and validate HTML forms

Few important fact to note:

- JavaScript is case-sensitive
- learning JavaScript is a pre-requisite to learning AJAX.
- JavaScript supports C-style comment // and /* */
- semicolon (;) is not required to end statements