HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>register error</title>
</head>
<body>
  <button id="run">Simulate error</button>
  <pre id="out">Click Simulate.</pre>
  <script>
    document.getElementById("run").addEventListener("click", function () {
      var out = document.getElementById("out");
      // Modern browsers lack register() — show equivalent error path
      if (!navigator.push && !("serviceWorker" in navigator)) {
        out.textContent = "Push register failed: NotSupportedError";
        return;
      }
      var fakeReq = {
        onsuccess: null,
        onerror: null,
        error: { name: "NotSupportedError", message: "register() removed — use subscribe()" }
      };
      fakeReq.onerror = function (event) {
        out.textContent = "Push register failed: " + event.target.error.name;
      };
      fakeReq.onerror({ target: fakeReq });
    });
  </script>
</body>
</html>

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register() — error handling (Try It)