HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>scrollBy() — log scrollY</title>
</head>
<body>
  <h1>Before / after scrollY</h1>
  <p>
    <button type="button" id="go">scrollBy(0, 100)</button>
    <button type="button" id="reset">Reset</button>
  </p>
  <pre id="out">Click scrollBy(0, 100)</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");
      document.getElementById("go").onclick = function () {
        var before = Math.round(window.scrollY || 0);
        window.scrollBy(0, 100);
        var after = Math.round(window.scrollY || 0);
        out.textContent = "Before: " + before + "\nAfter:  " + after;
      };
      document.getElementById("reset").onclick = function () {
        window.scrollTo(0, 0);
        out.textContent = "Reset to top\nscrollY: 0";
      };
    })();
  </script>
</body>
</html>

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