What Is DHTML?

Although often used as a synonym for JavaScript, DHTML is actually a combination of cascading style sheet and scripting technologies, built on top of basic HTML, which brings movement and interactivity to Web pages. (Some definitions also include embedded objects and applets.)

Cascading style sheets supply the ability to control the position and visibility of elements on the page. Scripting provides additional control over motion, layering, and visibility. Both react to user-input such as mouseovers, mouseclicks, and form-gathered information.

The cascading style sheet portion of DHTML draws primarily from CSS-P, the W3C standard for positioning variables, and CSS-2, which provides additional media-related items. If your users have Internet Explorer 4, you can safely call on the extremely helpful visibility and display characteristics of CSS; common positioning elements such as top, left, vertical align, and z-index (for three-dimensional layering); and a number of clever visual filters and transitions. Additional CSS elements are available in Internet Explorer 5, but this chapter will be confined to items requiring no more than IE 4.

The scripting component of DHTML may be written in JavaScript, JScript, or VBScript. This chapter works entirely with JavaScript. JavaScript is the de facto standard, supported by most of the common browsers, although VBScript is also widely used. The current JavaScript version 1.3 derives from ECMAScript, specifically from the ECMA-262 standards defined by the European Computer Manufacturers Association (ECMA). ECMA defines the standards for ECMAScript and, by extension, for JavaScript, just as the World Wide Web Consortium (W3C) defines the standards for HTML and CSS. (JScript is JavaScript with certain Internet Explorer-specific additions.)