In general, JavaScript should only be used to enhance functionality. It should never be used to provide key functionality. Furthermore, any JavaScript used should be cross-browser compatible. This can be most readily accomplished by using the subset of JavaScript known as ECMAScript (Specifically, ECMA-262 Edition 3)1) . If you do need to use browser-specific JavaScript, the web page or application should degrade gracefully when the page is viewed in a different browser without any impact on key functionality. When possible, a <noscript> section should also be used.