<!DOCTYPE html>
<html lang="en-US">
<body>
<p>Resize this window width and click 'run' button</p>
<p id="point"></p>
<p><strong>Note</strong>: use 'resize bar' between HTML Editor and the output window.</p>
<script>
var x = document.getElementById("point");
var txt = "This window width: "+window.innerWidth;
x.innerHTML = txt;
</script> </body>
</html>