The <script> and </script> HTML tags are used to enclose JavaScript code.

As the browser reads an HTML page, it executes any JavaScript code as it is read - with the exception of JavaScript functions which are run only when called (more on this later).

JavaScript programs can modify the content of a web page (text or images) but for security reasons are constrained from making any changes to the users PC. JavaScripts may not read/write files on the user's PC, cannot access user information nor send user information over the Internet.

HTML pages may contain multiple scripts. Variables created in one script are available to all other scripts on the page.

Generally, JavaScript is placed in the head of a page but JavaScript can actually be used in several different ways inside an HTML file:

1. Inline code (placed within <script> and </script> tags)

2. Event handlers (within other HTML tags, used to handle the web page response to a user event, such as clicking)

3. Replacement of attribute values (such replacing the URL value of the href attribute)

Some of the many uses of JavaScript include:

Navigation Display a frame in its own window Display popup messages Display popup windows Display hyperlinked menus Change status bar content Email a page to a visitor Disable use of right mouse click User Information write/read cookies browser ID determine screen size Web Sites create a guestbook bookmark a page add URL to favorites send URL to a friend count # of visits get user IP address print this page

Applications clock calendar calculation color picker ramdom message Visual Effects mouseovers slideshow animation images watermark banners background images text effects mouse cursors Games/Humor Moving eyes Bouncing balls Security passwords