Returns -1, as there is no element with ID foobar.

Edit code and click me	Your Result (Some examples do not work in Google Chrome):
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <style>div { font-weight: bold; color: #090; }</style> <script src="http://code.jquery.com/jquery-latest.js"></script> <script type="text/javascript" language="javascript"> $(document).ready(function(){ var foobar = $("li").index( $('#foobar') ); $('div').html('Index: ' + foobar); }); </script> </head> <body> <ul> <li id="foo">foo</li> <li id="bar">bar</li> <li id="baz">baz</li> </ul> <div></div> </body> </html>
Edit the code above and click to see the result	www.xhtml.co.il - Try it yourself