HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>preferences — helper</title>
</head>
<body>
  <button id="btn" type="button">Snapshot</button>
  <pre id="out">Click Snapshot</pre>
  <script>
    function preferencesSnapshot() {
      if (!navigator.preferences) {
        return { ok: false, reason: "api-missing" };
      }
      var keys = [
        "colorScheme",
        "contrast",
        "reducedMotion",
        "reducedTransparency",
        "reducedData"
      ];
      var values = {};
      for (var i = 0; i < keys.length; i++) {
        var key = keys[i];
        try {
          var obj = navigator.preferences[key];
          values[key] = obj && "value" in obj ? obj.value : null;
        } catch (err) {
          values[key] = null;
        }
      }
      return { ok: true, values: values };
    }
    document.getElementById("btn").addEventListener("click", function () {
      document.getElementById("out").textContent =
        JSON.stringify(preferencesSnapshot(), null, 2);
    });
  </script>
</body>
</html>

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preferences — snapshot helper (Try It)