HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>scrollTo() — log scrollY</title>
</head>
<body>
  <h1>Before / after scrollY</h1>
  <p>
    <button type="button" id="go">scrollTo(0, 300)</button>
    <button type="button" id="again">scrollTo(0, 300) again</button>
  </p>
  <pre id="out">Click scrollTo(0, 300)</pre>
  <p>Top of page</p>
  <p><br><br><br><br><br><br><br><br><br><br></p>
  <p><br><br><br><br><br><br><br><br><br><br></p>
  <p><br><br><br><br><br><br><br><br><br><br></p>
  <p><br><br><br><br><br><br><br><br><br><br></p>
  <p>Bottom of page</p>
  <script>
    (function () {
      var out = document.getElementById("out");
      function jump() {
        var before = Math.round(window.scrollY || 0);
        window.scrollTo(0, 300);
        var after = Math.round(window.scrollY || 0);
        out.textContent =
          "Before: " + before +
          "\nAfter:  " + after +
          "\n(same target each time — not additive)";
      }
      document.getElementById("go").onclick = jump;
      document.getElementById("again").onclick = jump;
    })();
  </script>
</body>
</html>

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JavaScript Window scrollTo() — log scrollY (Try It)