//a big thank to JavaScript Kit (http://www.javascriptkit.com)
//for a valid implementation of external css sheet
function loadjscssfile(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);
}
if (typeof fileref!="undefined")
document.getElementsByTagName("head")[0].appendChild(fileref)
}

var filesadded="" //list of files already added

function checkloadjscssfile(filename, filetype){
if (filesadded.indexOf("["+filename+"]")==-1){
loadjscssfile(filename, filetype)
filesadded+="["+filename+"]" //add to list of files already added, in the form of "[filename1],[filename2],etc"
}
else
alert("file already added!")
}