To get the class of an element with JavaScript you use the className property of the element object. Take the following section of HTML code.

Use the following bit of code to print off the class name of the div element in a message box.

A good usability feature of web forms is to fill the contents of one drop down menu, depending on what has been selected in a previous menu. This can be done quite easily with JavaScript.

Take the following form, in this instance I have used some server variables used in mod_rewrite, but the idea is valid.

If you have lots of check boxes in a row a handy little usability trick is to allow a user to click on a button and check all of the checkboxes at once. The following function will either check or uncheck all of the check boxes in your form.

Creating a form as part of an AJAX control is a common practice, but when you include a submit button within the form the default behaviour of the form is to redirect to the destination supplied in action. To run a form using JavaScript you need to include two things.

In order to overwrite the normal operation of a form you will need to replace the action attribute with some JavaScript code that returns false. This is can be done in the form of come in-line JavaScript code (commonly called a bookmarklet) in the place of any URL in the action attribute of the form.

When writing JavaScript applications I normally write for loops like this.

Detecting the user agent in JavaScript can be important due to the way in which different browsers implement JavaScript. Sometimes it is necessary to create logic to do one thing in Firefox and another thing in IE. Luckily, all modern browsers support the navigator.userAgent property so that is a good start.

Because it is possible to mask your user agent in Opera it is necessary to detect this browser first. There are actually two different ways to hide the user agent in Opera. The default user agent is as follows: