Android - PWA does not open in standalone mode with service worker

Question

While developing a Progressive-Web-App the following Problem occurred:

Standalone mode works perfectly without including the service worker - but does NOT work with.

Without Service-Worker a2hs (added to Homescreen) PWA gets correctly started in "standalone"-Mode.
After adding the Service-Worker (a2hs + installed / Web-APK) PWA opens new Tab in new Chrome-Window.

Chrome-PWA-Audit:

login_mobile_tablet.jsf / include service worker:

<script>
    if ('serviceWorker' in navigator) {
        navigator.serviceWorker.register('../serviceWorker.js', {scope: "/application/"})
          /* also tried ".", "/", "./" as scope value */
            .then(function(registration) {
                console.log('Service worker registration successful, scope is: ', registration.scope);
            })
            .catch(function(error) {
                console.log('Service worker registration failed, error: ', error);
            });
    }
</script>

serviceWorker.js:

var cacheName = 'pwa-cache';

// A list of local resources we always want to be cached.
var filesToCache = [
    'QS1.xhtml',
    'pdf.xhtml',
    'QS1.jsf',
    'pdf.jsf',
    'login_pages/login_mobile_tablet.jsf',
    'login_pages/login_mobile_tablet.xhtml'
];

// The install handler takes care of precaching the resources we always need.
self.addEventListener('install', function(event) {

    event.waitUntil(
        caches.open(cacheName).then(function(cache) {
            return cache.addAll(filesToCache);
        })
    );
})

// The activate handler takes care of cleaning up old caches.
self.addEventListener('activate', event => {
    event.waitUntil(self.clients.claim());
});

// The fetch handler serves responses for same-origin resources from a cache.
self.addEventListener('fetch', event => {

    // Workaround for error:
    // TypeError: Failed to execute 'fetch' on 'ServiceWorkerGlobalScope': 'only-if-cached' can be set only with 'same-origin' mode
    // see: https://stackoverflow.com/questions/48463483/what-causes-a-failed-to-execute-fetch-on-serviceworkerglobalscope-only-if
    if (event.request.cache === 'only-if-cached' && event.request.mode !== 'same-origin')
        return;

    event.respondWith(
        caches.match(event.request, {ignoreSearch: true})
            .then(response => {
                return response || fetch(event.request);
            })
    );
});

manifest.json:

{
   "name":"[Hidden]",
   "short_name":"[Hidden]",
   "start_url":"/application/login_pages/login_mobile_tablet.jsf",
   "scope":".",
   "display":"standalone",
   "background_color":"#4688B8",
   "theme_color":"#4688B8",
   "orientation":"landscape",
   "icons":[
      {
         "src":"javax.faces.resource/images/icons/qsc_128.png.jsf",
         "sizes":"128x128",
         "type":"image/png"
      },
      {
         "src":"javax.faces.resource/images/icons/qsc_144.png.jsf",
         "sizes":"144x144",
         "type":"image/png"
      },
      {
         "src":"javax.faces.resource/images/icons/qsc_152.png.jsf",
         "sizes":"152x152",
         "type":"image/png"
      },
      {
         "src":"javax.faces.resource/images/icons/qsc_192.png.jsf",
         "sizes":"192x192",
         "type":"image/png"
      },
      {
         "src":"javax.faces.resource/images/icons/qsc_256.png.jsf",
         "sizes":"256x256",
         "type":"image/png"
      },
      {
         "src":"javax.faces.resource/images/icons/qsc_512.png.jsf",
         "sizes":"512x512",
         "type":"image/png"
      }
   ]
}

The following questions / answers were considered - but no solution was found:

score 2 · Accepted Answer · answered Jan 18 '19 at 06:49

Technical Background
The Moment you add your Service-Worker (along all other PWA-Requirements) your App gets created as an Real PWA - with Web-APK getting installed. Therefore you also need to use Default-HTTPS-Port 443 - make sure you use a valid HTTPS-Certificate.
Before adding the Service-Worker, this mandatory requirement was missing so your PWA was NOT installed and therefore needed less other requirements to be displayed in "standalone-mode".
It's just a shame that this is nowhere documented... and we had to "find out" for ourselves.

Short-List of Mandatory Requirements for "Installable Web-APK":
(As we could not find a full List, i try to include all Points)

Registered Service-Worker (default-implementation like yours is enough)
manifest.json (yours is valid)
https with valid certificate
https default-port (443, eg. https://yourdomain.com/test/)
... for the rest just check chrome audit tool (HINT: you don't need to pass all requirements - your web-apk should work when switching to https-default-port)

Android - PWA does not open in standalone mode with service worker

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