Remove last element from url

Here is a slightly simpler way:

url = url.slice(0, url.lastIndexOf('/'));

as simple as this:

var to = url.lastIndexOf('/');
to = to == -1 ? url.length : to + 1;
url = url.substring(0, to);

$('span').attr('st_url', function(i, url) {
    var str = url.substr(url.lastIndexOf('/') + 1) + '$';
    return url.replace( new RegExp(str), '' );
});

DEMO