Extract URL's directory from path, without file name such as “index.html”

Question

I am looking for plain JavaScript code (no jQuery etc.) to learn the directory path component of my currently loaded page\'s URL.

For instance, if my page is loaded

Answer 1

It looks like this does the trick:

var href = window.location.href;
var dir = href.substring(0, href.lastIndexOf('/')) + "/";

Is this a safe method or can this fail with more complex URLs?