HTML Code
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>PushEvent data safe</title>
</head>
<body>
  <button id="run">Run in service worker</button>
  <pre id="out">Click Run (needs HTTPS or localhost).</pre>
  <script>
    document.getElementById("run").addEventListener("click", function () {
      var out = document.getElementById("out");
      if (!window.isSecureContext || !("serviceWorker" in navigator)) {
        out.textContent = "Need secure context + serviceWorker.";
        return;
      }
      var sw = [
        "self.addEventListener('install',function(e){self.skipWaiting();});",
        "self.addEventListener('activate',function(e){e.waitUntil(self.clients.claim());});",
        "self.addEventListener('message',function(e){",
        "  if(e.data!=='run')return;",
        "  var evt=new PushEvent('push');",
        "  var payload=evt.data?evt.data.json():{};",
        "  var title=payload.title??'Default title';",
        "  var count=payload.count??0;",
        "  e.source.postMessage(title+' '+count);",
        "});"
      ].join("");
      var url = URL.createObjectURL(new Blob([sw], { type: "application/javascript" }));
      var reg;
      navigator.serviceWorker.register(url).then(function (r) {
        reg = r;
        return navigator.serviceWorker.ready;
      }).then(function (readyReg) {
        return new Promise(function (resolve) {
          navigator.serviceWorker.addEventListener("message", function fn(ev) {
            navigator.serviceWorker.removeEventListener("message", fn);
            resolve(ev.data);
          });
          (readyReg.active || readyReg.installing).postMessage("run");
        });
      }).then(function (text) {
        out.textContent = text;
        if (reg) reg.unregister();
        URL.revokeObjectURL(url);
      }).catch(function (err) {
        out.textContent = "Error: " + err.message;
        URL.revokeObjectURL(url);
      });
    });
  </script>
</body>
</html>
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PushEvent.data — optional chaining (Try It)
