Introduction to Dynamic HTML
By Aaron Weiss
Dynamic HTML builds upon existing HTML standards to expand the possibilities of Web page design, presentation, and interaction. Ultimately, mastering DHTML will allow you to build Web-based applications, rather than mere portraits of data. Because DHTML is essentially an "added value" technology, you should be rather familiar with basic Web page design using traditional HTML specifications. Experience with JavaScript programming is also necessary to employ the potential of DHTML. Consequently, portions of this introduction to DHTML will assume some HTML and JavaScript familiarity.
What and Why
The Web is an ever evolving environment, and Web pages themselves are steadily blooming from static displays of data to interactive applications. "Dynamic HTML" is somewhat of an umbrella term encompassing several ways in which Web developers can breathe life into pages which have traditionally been still portraits of information.
The basic notion behind Dynamic HTML is quite simple: allow any element of a page to be changeable at any time. Sounds like a dream, but as with any simple plan, "God is in the details," as they say. In the olden days, you could only change content on a page via CGI. This required a server to perform the changes to the page and re-serve the entire page, modifications and all, back to the client. While workable, this process was quite slow, as it placed a burden on both network traffic and server processing time. With long delays between a user's action and an on-screen response, building effective Web-based applications was quite constricting.
With DHTML, the magic occurs entirely on the client-side. This means that page modifications should appear immediately following a trigger, such as a user selection. And, remember, the DHTML dream is that you can modify any aspect of the currently loaded page -- text styles, swapped images, context-sensitive forms and tables, and even the on-screen data itself.
It's worth noting here, then, that "Dynamic HTML," isn't really about HTML, the markup language. By and large, DHTML describes the abstract concept of breaking up a page into manipulable elements, and exposing those elements to a scripting language which can perform the manipulations. The degree, or fineness, to which these elements are defined and actionable is a function of DHTML's maturity. And since it has only been around for a year or so, DHTML is not fully mature.
Like the Web itself, Dynamic HTML is ever evolving. At some point, DHTML may self actualize and reach its full potential of "change anything anywhere anytime." It may even change its name -- product developers possess a whimsy for this sort of thing -- but the concepts defined above for modifying elements on a page will necessarily continue to mature.
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