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<!DOCTYPE html>

<html lang="en">

<head>

  <meta charset="utf-8">

  <title>Invalid Date</title>

</head>

<body>

  <h1>Invalid UTC string</h1>

  <pre id="out"></pre>

  <script>

    var bad = new Date("not-a-date");

    var lines = [bad.toUTCString()];

    if (Number.isNaN(bad.getTime())) {

      lines.push("Cannot format UTC string");

    }

    document.getElementById("out").textContent = lines.join("\n");

  </script>

</body>

</html>

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JavaScript Date toUTCString() — invalid Date (Try It)