Javascript for dynamic script and css loading with cache buster

index.html

<script>
    (function(d){
        var s = d.createElement('link');
        d.getElementsByTagName('head')[0].appendChild(s);
        s.setAttribute('type', 'text/css');
        s.setAttribute('rel', 'stylesheet');
        s.setAttribute('href', 'app.css?v='+(new Date()).getTime());


        var s = d.createElement('script');
        d.getElementsByTagName('head')[0].appendChild(s);
        s.src = 'app.js?v='+(new Date()).getTime();
        s.onload = function(){
            nowScriptIsReady()
        }
        s.onreadystatechange= function () {
            if (this.readyState == 'complete') {
                nowScriptIsReady()
            }
       }
    })(document)
</script>