<script type='text/javascript'>
//<![CDATA[
var downloadButton = document.getElementById("download");
var counter = 5;
var newElement = document.createElement("p");
newElement.innerHTML = "";
var id;
downloadButton.parentNode.replaceChild(newElement, downloadButton);
function startDownload() {
    this.style.display = 'none';
    id = setInterval(function () {
        counter--;
        if (counter < 0) {
            newElement.parentNode.replaceChild(downloadButton, newElement);
            clearInterval(id);
        } else {
            newElement.innerHTML = +counter.toString() + " second.";
        }
    }, 1000);
};
var clickbtn = document.getElementById("btn");
clickbtn.onclick = startDownload;
//]]>
</script>