ServiceWorker

if ("serviceWorker" in navigator) {
  navigator.serviceWorker
    .register("service-worker.js", {
      scope: "./",
    })
    .then(function (registration) {
      var serviceWorker;
      if (registration.installing) {
        serviceWorker = registration.installing;
        document.querySelector("#kind").textContent = "installing";
      } else if (registration.waiting) {
        serviceWorker = registration.waiting;
        document.querySelector("#kind").textContent = "waiting";
      } else if (registration.active) {
        serviceWorker = registration.active;
        document.querySelector("#kind").textContent = "active";
      }
      if (serviceWorker) {
        // logState(serviceWorker.state);
        serviceWorker.addEventListener("statechange", function (e) {
          // logState(e.target.state);
        });
      }
    })
    .catch(function (error) {
      //     Service Worker.
      //  service-worker.js       .
    });
} else {
  //     Service Worker.
}