Web Design in a Nutshell, 3rd Edition

Programming

The standards that govern web behaviors are the scripting language ECMAScript (so close to JavaScript 1.5 that it is usually just referred to by the less technical sounding moniker, JavaScript) and the Document Object Model (DOM), which defines the components of a web page that can be manipulated.

There is the same good news/bad news scenario for JavaScript and the DOM. Although 99% of compliant browsers profess to support the standards, they are fraught with bugs and inconsistencies. Some browsers do not support certain JavaScript functions. Microsoft has added its own extensions to the DOM that work only in Internet Explorer. And so on.

For the remaining 1% of browsers that do not support the DOM at all (namely Version 4 browsers), there are no simple workarounds. It is usually necessary to serve an alternative version of the page that uses scripting functions those browsers can understand, or to provide an explanatory page without scripts at all that would work on any browser.