Dynamic HTML and Scriptlets Add Life

Differences aside, both Microsoft and Netscape browsers let pages change on the fly.

Rick Dobson

Dynamic Web pages promise content creators more precise rendering of their material and promise users more customized and interesting interfaces. Dynamic HTML (DHTML), the technology behind dynamic Web pages, offers faster-performing pages by eliminating the need to download pages for altered content, different styles, object repositioning, or data manipulation. Also, its Document Object Model (DOM) delivers highly graphic and interactive pages, because it converts all HTML elements to objects.

Each element exposes properties a nd methods that can enliven Web pages. A rich event model lets elements interact with their parents as well as page visitors. Content authors can also use scripting languages, such as ECMA-262 (European Computer Manufacturers Association) JavaScript and Microsoft VBScript, to animate their pages by manipulating properties, invoking methods, and responding to events. Event bubbling makes it possible to write one function to process events from many objects. Commercial component builders can design advanced tools with languages such as Java or C++.

Microsoft introduced Scriptlets with the final release of Internet Explorer 4. This technology lets DHTML developers create components for reuse by other Web authors. These DHTML-based components also serve as Component Object Model (COM) objects that any COM container, even Word, can run ( see the table ).

The W3C issued a series of preliminary specifications in 1997 that cover cascading style sheet s (CSS), CSS positioning, and the DOM. The W3C will finalize its DHTML specifications in 1998. During 1997, both Microsoft and Netscape committed to an "interoperability pledge," which states among other things that their browsers will comply with W3C final specifications. Until -- and even after -- the browsers comply with the final specifications, HTML authors will face compatibility issues.

Both browsers have technology that relates to DHTML but is outside its immediate scope. Netscape browsers permit positioning with their Layers technology as well as the W3C positioning coordinates. The Layers approach is incompatible with the W3C specification. Microsoft's Scriptlets technology requires some code that is not part of Netscape browsers at the time of this writing. Because Scriptlets are an application of DHTML, they are beyond the scope of the interoperability pledge.

DHTML poses challenges for Web-site developers. There is the issue of incorporating the new technology into Web pages. This is more than learning a few scripting instructions and some HTML element properties, methods, and events. It includes making trade-offs between direct authoring versus relying on applets and components. Direct authoring promises faster downloading of pages and more customization, but using applets and components allows shared access to advanced developer skills.

Should Web developers bother learning DHTML? You decide after contrasting your static HTML site with a competitor's DHTML site.

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Where to Find

W3C

Cambridge, MA
Phone:    617-253-2613
Internet: 
http://www.w3.org




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A Tale of Two DHTMLs

A Tale of Two DHTMLs
Netscape DHTML in Navigator 4.0	Microsoft DHTML in Internet Explorer 4
Lets scripts access style sheet data, but you cannot change styles after the page loads.	Scripts can change page-element properties after load time.
Scripts can access properties of some page elements.	Scripts can access properties of every page element.
Animation via script manipulation of CSS-positioning data.	Animation via script manipulation of CSS-positioning data.
Layers-tags are used to section HTML pages into separate units that you can position as desired at any pixel coordinates on the page -- can be loaded with new data from a new URL after load time.	Scriptlets can alter the HTML that comprises the page; these components can also serve as COM objects and be used by any COM container, such as Microsoft Word; complementary to DHTML, scriptlets won't be part of the W3C standard.

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W3C in 1998

illustration_link (11 Kbytes)

AT A GLANCE: DHTML is an object-oriented HTML that can make pages faster, livelier, and more interactive than your old HTML.

WHO SUPPORTS IT: Micro soft, W3C, Netscape, SoftQuad.