function createInclude(filename, filetype) {
    if (filetype == "js") { //if filename is a external JavaScript file
        var fileref = document.createElement('script');
        fileref.setAttribute("type", "text/javascript");
        fileref.setAttribute("src", filename);
    }
    else if (filetype == "css") { //if filename is an external CSS file
        var fileref = document.createElement("link");
        fileref.setAttribute("rel", "stylesheet");
        fileref.setAttribute("type", "text/css");
        fileref.setAttribute("href", filename);
    }
    return fileref;
}

function addInclude(filename, filetype)
{
    var include = createInclude(filename, filetype);
    document.getElementsByTagName("head")[0].appendChild(include);
}

function replaceInclude(oldfilename, newfilename, filetype) {
    var targetelement = (filetype == "js") ? "script" : (filetype == "css") ? "link" : "none"; //determine element type to create nodelist using
    var targetattr = (filetype == "js") ? "src" : (filetype == "css") ? "href" : "none";  //determine corresponding attribute to test for
    var allsuspects = document.getElementsByTagName(targetelement);
    for (var i = allsuspects.length; i >= 0; i--) { //search backwards within nodelist for matching elements to remove
        if (allsuspects[i] && allsuspects[i].getAttribute(targetattr) != null && allsuspects[i].getAttribute(targetattr).indexOf(oldfilename) != -1) {
            var newelement = createInclude(newfilename, filetype);
            allsuspects[i].parentNode.replaceChild(newelement, allsuspects[i]);
        }
    }
}