<!DOCTYPE html>
<html>
<body>

<p>Click the button to display the width of your screen, in pixels.</p>

<button onclick="myFunction()">Try it</button>

<p id="demo"></p>

<script>
function myFunction() {
  var x = "Width: " + screen.width + "px";
  document.getElementById("demo").innerText = x;
}
</script>

</body>
</html>