HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>onvisibilitychange</title>
  <style>
    #out { border: 1px solid #ccc; padding: 10px; }
  </style>
</head>
<body>
  <p>Leave this tab and return to update the status line.</p>
  <pre id="out">(checking)</pre>
  <script>
    var out = document.getElementById("out");
    function render() {
      out.textContent =
        "Now: " + document.visibilityState +
        " (hidden=" + document.hidden + ")";
    }
    document.onvisibilitychange = render;
    render();
  </script>
</body>
</html>

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Document visibilitychange — onvisibilitychange (Try It)