function highlightLink() {
    //Get filename from the URL
    thisPage = document.URL.substring(document.URL.lastIndexOf("/")+1 ,document.URL.length);

    //Loop through all the links
    for (i=0; i<document.links.length; i++ ) {
        //Get only the filename from the href of navigation link
        pageLink = document.links[i].href.substring(document.links[i].href.lastIndexOf("/")+1 ,document.links[i].href.length);

        //if the current filename & the link-ed file name are the same, change the background color of that link
        if (thisPage == pageLink) {
            //BG is the name of a class that I have defined, that sets background color to grey
            document.links[i].className += " active";
        }
    }
}