<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <style>
      body {
        height: 10000px;
        margin: 0;
      }
      p {
        position: absolute;
        margin: 0;
      }
    </style>
    <script>
      window.onload = () => {
        window.parent.postMessage({
          url: window.location.toString(),
          scrollY: window.scrollY
        }, "*");
      }
    </script>
  </head>
  <body>
    <p style="top: 2000px" id="target">Target</p>
    <p style="top: 4000px" id="fromRedirect">Target</p>
  </body>
</html>