script.js

const divInstall = document.getElementById("installContainer");
const butInstall = document.getElementById("butInstall");

/* Put code here */
window.addEventListener("beforeinstallprompt", event => {
  console.log("👍", "beforeinstallprompt", event);
  // Stash the event so it can be triggered later.
  window.deferredPrompt = event;
  // Remove the 'hidden' class from the install button container
  divInstall.classList.toggle("hidden", false);
});

butInstall.addEventListener("click", async () => {
  console.log("👍", "butInstall-clicked");
  const promptEvent = window.deferredPrompt;
  if (!promptEvent) {
    // The deferred prompt isn't available.
    return;
  }
  // Show the install prompt.
  promptEvent.prompt();
  // Log the result
  const result = await promptEvent.userChoice;
  console.log("👍", "userChoice", result);
  // Reset the deferred prompt variable, since
  // prompt() can only be called once.
  window.deferredPrompt = null;
  // Hide the install button.
  divInstall.classList.toggle("hidden", true);
});

window.addEventListener("appinstalled", event => {
  console.log("👍", "appinstalled", event);
  // Clear the deferredPrompt so it can be garbage collected
  window.deferredPrompt = null;
});

/* Only register a service worker if it's supported */
if ("serviceWorker" in navigator) {
  navigator.serviceWorker.register("service-worker.js");
}

/**
 * Warn the page must be served over HTTPS
 * The `beforeinstallprompt` event won't fire if the page is served over HTTP.
 * Installability requires a service worker with a fetch event handler, and
 * if the page isn't served over HTTPS, the service worker won't load.
 */
if (window.location.protocol === "http:") {
  const requireHTTPS = document.getElementById("requireHTTPS");
  const link = requireHTTPS.querySelector("a");
  link.href = window.location.href.replace("http://", "https://");
  requireHTTPS.classList.remove("hidden");
}