<!DOCTYPE html>
<html lang="en">
<head>
<title>Window Size Display</title>
</head>
<body>
<script>
function displayWindowSize() {
document.body.innerHTML = 'Window width: ' + window.innerWidth + 'px<br>Window height: ' + window.innerHeight + 'px';
}
window.onresize = displayWindowSize;
window.onload = displayWindowSize;
</script>
</body>
</html>