<span id="q"></span>
<input type='button' onClick='Ok()' value='Ok' id="Ok">
<script>
document.addEventListener("DOMContentLoaded", function Ok() {
var title = sessionStorage.getItem("mes");
var div = document.getElementById("q");
var btn = document.getElementById("Ok");
var oldTitle = div.innerHTML;
if (title) div.innerHTML = title;
btn.addEventListener("click", function() {
title =prompt("Сообщение:", "");
if(title === null) title = oldTitle ;
div.innerHTML = sessionStorage.mes = title
})
});
</script>
вроде работает
