How might I get the script filename from within that script?

var scripts = document.getElementsByTagName('script');
var lastScript = scripts[scripts.length-1];
var scriptName = lastScript.src;
alert("loading: " + scriptName);

Tested in: FF 3.0.8, Chrome 1.0.154.53, IE6

See also: How may I reference the script tag that loaded the currently-executing script?