HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>visibilitychange log</title>
  <style>
    #log { white-space: pre-wrap; border: 1px solid #ccc; padding: 10px; min-height: 80px; }
  </style>
</head>
<body>
  <p>Switch to another tab, then come back. Watch the log.</p>
  <pre id="log">(waiting)</pre>
  <script>
    var log = document.getElementById("log");
    log.textContent = "Start: " + document.visibilityState + "\n";
    document.addEventListener("visibilitychange", function () {
      log.textContent +=
        "visibilityState: " + document.visibilityState + "\n";
    });
  </script>
</body>
</html>

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Document visibilitychange — log visibilityState (Try It)