<!doctype html>
<html>
  <head>
    <meta charset="UTF-8">
    <title>Page recording its size</title>
  </head>
  <body>
    <script>
      var initialSize = { width: innerWidth, height: innerHeight };
      var loadSize;
      onload = () => {
        loadSize = { width: innerWidth, height: innerHeight };
      };
    </script>
  </body>
</html>
