HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>hasFocus visibility</title>
  <style>body{font-family:system-ui,sans-serif;padding:1.5rem;} pre{border:1px solid #ccc;padding:0.75rem;}</style>
</head>
<body>
  <p>Click Read, then switch tabs and come back to compare values.</p>
  <button id="btn" type="button">Read focus + visibility</button>
  <pre id="out">Click the button</pre>
  <script>
    function snapshot() {
      document.getElementById("out").textContent = JSON.stringify({
        hasFocus: document.hasFocus(),
        visibilityState: document.visibilityState,
        hidden: document.hidden
      }, null, 2);
    }
    document.getElementById("btn").addEventListener("click", snapshot);
    document.addEventListener("visibilitychange", snapshot);
  </script>
</body>
</html>

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Document.hasFocus — with visibility (Try It)