jQuery.getScript(url,[callback])

function loadJs(name) {

    document.write('<script src="'+name+'" type="text/javascript"></script>');

}

function loadjscssfile(filename,filetype){

    if(filetype == "js"){

        var fileref = document.createElement('script');

        fileref.setAttribute("type","text/javascript");

        fileref.setAttribute("src",filename);

    }else if(filetype == "css"){

        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);

    }

}

loadjscssfile("do.js","js");