Angular PWA does not work when change to OFFLINE and press Refresh (F5)

Question

I'm using angular to make PWA app.

• Angular: 12

What is going on is:

• I go to my app (online mode) -> The web app can display properly
• Turn on developer console and change connectivity to OFFLINE
• Press F5 to reload the application

What happens:

• The below image is what it displays on the screen when I hit reload:

This is my ngsw-config.json

{
  "$schema": "../../node_modules/@angular/service-worker/config/schema.json",
  "index": "/index.html",
  "assetGroups": [
    {
      "name": "app",
      "installMode": "prefetch",
      "resources": {
        "files": [
          "/favicon.ico",
          "/index.html",
          "manifest.json",
          "/*.css",
          "/*.js"
        ]
      }
    },
    {
      "name": "assets",
      "installMode": "lazy",
      "updateMode": "prefetch",
      "resources": {
        "files": [
          "/assets/**",
          "/*.(eot|svg|cur|jpg|png|webp|gif|otf|ttf|woff|woff2|ani)"
        ]
      }
    }
  ]
}

• manifest.json

{
  "name": "ng-main",
  "short_name": "ng-main",
  "theme_color": "#1976d2",
  "background_color": "#fafafa",
  "display": "standalone",
  "scope": "./",
  "start_url": "./",
  "icons": [
    {
      "src": "assets/icons/icon-72x72.png",
      "sizes": "72x72",
      "type": "image/png",
      "purpose": "maskable any"
    },
    {
      "src": "assets/icons/icon-96x96.png",
      "sizes": "96x96",
      "type": "image/png",
      "purpose": "maskable any"
    },
    {
      "src": "assets/icons/icon-128x128.png",
      "sizes": "128x128",
      "type": "image/png",
      "purpose": "maskable any"
    },
    {
      "src": "assets/icons/icon-144x144.png",
      "sizes": "144x144",
      "type": "image/png",
      "purpose": "maskable any"
    },
    {
      "src": "assets/icons/icon-152x152.png",
      "sizes": "152x152",
      "type": "image/png",
      "purpose": "maskable any"
    },
    {
      "src": "assets/icons/icon-192x192.png",
      "sizes": "192x192",
      "type": "image/png",
      "purpose": "maskable any"
    },
    {
      "src": "assets/icons/icon-384x384.png",
      "sizes": "384x384",
      "type": "image/png",
      "purpose": "maskable any"
    },
    {
      "src": "assets/icons/icon-512x512.png",
      "sizes": "512x512",
      "type": "image/png",
      "purpose": "maskable any"
    }
  ]
}

Answer 1

After having spent hours searching for solutions I noticed when I built my app using ng build --configuration production. There is one ngsw.json file inside my dist folder.

However, the urls and patterns in the generated ngsw.json file are all empty, like the one below:

"assetGroups": [
    {
        "name": "app",
        "installMode": "prefetch",
        "updateMode": "prefetch",
        "cacheQueryOptions": {
            "ignoreVary": true
        },
        "urls": [],
        "patterns": []
    },
    {
        "name": "assets",
        "installMode": "lazy",
        "updateMode": "prefetch",
        "cacheQueryOptions": {
            "ignoreVary": true
        },
        "urls": [],
        "patterns": []
    }
]

When I added the urls to cache in assetGroups and tried again, the application worked smoothly. (Please see the content below)

"assetGroups": [
    {
        "name": "app",
        "installMode": "prefetch",
        "updateMode": "prefetch",
        "cacheQueryOptions": {
            "ignoreVary": true
        },
        "urls": [
            "/login",
            "/dashboard"
        ],
        "patterns": [
            "/*.css",
            "/*.js"
        ]
    },
    {
        "name": "assets",
        "installMode": "lazy",
        "updateMode": "prefetch",
        "cacheQueryOptions": {
            "ignoreVary": true
        },
        "urls": [
            "/favicon.ico",
            "/index.html",
            "/manifest.webmanifest",
            "/ngsw.json"
        ],
        "patterns": []
    }
]

I already reported to Angular team about this and it has been confirmed as a bug in Angular 12.

In conclusion, now, I have to workaround by copying the ngsw.json file with the cached urls in assetGroups, after having built the application, I copy that ngsw.json to the dist folder.

Answer 2

but in my case the URLs are not empty in the ngsw.json at dist/myproject but still in offline mode it not working. throwing the error

The Error is

 ngsw.json URL: http://127.0.0.1:8080/ngsw.json?ngsw-cache-bust=0.2758348374356183

Error: net::ERR_INTERNET_DISCONNECTED Fetch: ngsw-worker.js:2925 Size: 0 B Time: 3 ms