HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>scroll progress</title>
  <style>
    #scroll-box {
      overflow: auto; height: 120px; width: 220px;
      border: 2px solid #333;
    }
    #scroll-box .inner { height: 480px; padding: 8px; }
  </style>
</head>
<body>
  <div id="scroll-box"><div class="inner">Scroll to the bottom…</div></div>
  <pre id="out">progress=0%</pre>
  <script>
    var box = document.getElementById("scroll-box");
    var out = document.getElementById("out");
    box.addEventListener("scroll", function () {
      var max = box.scrollHeight - box.clientHeight;
      var pct = max > 0 ? Math.round((box.scrollTop / max) * 100) : 0;
      out.textContent = "progress=" + pct + "%";
    });
  </script>
</body>
</html>

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Element scroll — progress percent (Try It)