IE and Firefox both contain ways to execute JavaScript from CSS. As Paolo mentions, one way in IE is the expression technique, but there's also the more obscure HTC behaviour, in which a separate XML that contains your script is loaded via CSS. A similar technique for Firefox exists, using XBL. These techniques don't execute JavaScript from CSS directly, but the effect is the same.
HTC with IE
Use a CSS rule like so:
body {
behavior:url(script.htc);
}
and within that script.htc file have something like:
<PUBLIC:COMPONENT TAGNAME="xss">
<PUBLIC:ATTACH EVENT="ondocumentready" ONEVENT="main()" LITERALCONTENT="false"/>
</PUBLIC:COMPONENT>
<SCRIPT>
function main()
{
alert("HTC script executed.");
}
</SCRIPT>
The HTC file executes the main() function on the event ondocumentready (referring to the HTC document's readiness.)
XBL with Firefox
Firefox supports a similar XML-script-executing hack, using XBL.
Use a CSS rule like so:
body {
-moz-binding: url(script.xml#mycode);
}
and within your script.xml:
<?xml version="1.0"?>
<bindings xmlns="http://www.mozilla.org/xbl" xmlns:html="http://www.w3.org/1999/xhtml">
<binding id="mycode">
<implementation>
<constructor>
alert("XBL script executed.");
</constructor>
</implementation>
</binding>
</bindings>
All of the code within the constructor tag will be executed (a good idea to wrap code in a CDATA section.)
In both techniques, the code doesn't execute unless the CSS selector matches an element within the document. By using something like body, it will execute immediately on page load.
