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static/public/index.js

@@ -273,4 +273,18 @@ function changeFavicon(src) {
      document.head.removeChild(oldLink);
     }
     document.head.appendChild(link);
-   }
+   }
+
+// This variable will save the event for later use.
+let deferredPrompt;
+window.addEventListener('beforeinstallprompt', (e) => {
+  // Prevents the default mini-infobar or install dialog from appearing on mobile
+  e.preventDefault();
+  // Save the event because you'll need to trigger it later.
+  deferredPrompt = e;
+  // Show your customized install prompt for your PWA
+  // Your own UI doesn't have to be a single element, you
+  // can have buttons in different locations, or wait to prompt
+  // as part of a critical journey.
+  showInAppInstallPromotion();
+});