This snippet will get the filename from the url. The filename is the last part of the URL from the last trailing slash. For example, if the URL is http://www.example.com/dir/file.html then file.html is the file name.
Explanation
var url = window.location.pathname;
This declares the url variable and adds the current pathname as its value.
var filename = url.substring(url.lastIndexOf('/')+1);
alert(filename);
substring (method) - extract characters from start (parameter). url is the stringObject url.substring(start)
lastIndexOf (method) - position of last occurrence of specified string value, in this case the ‘/’
Add one to lastIndexOf because we do not want to return the ‘/’
Full snippet
var url = window.location.pathname;
var filename = url.substring(url.lastIndexOf('/')+1);
alert(filename);