Finally, code updateSale(); to call the function and update the item.

<html>
<body>
<h1 id="sale">Sale!</h1>
<script>
var saleItem = "Shirt";

function updateSale() {
var sale = document.getElementById("sale").innerHTML;
var update = saleItem + " " + sale;
document.getElementById("sale").innerHTML = update;
}

updateSale();
</script>
</body>
</html>]]>

Make sure to code updateSale();