Publishing a Progressive Web App

Because Ionic Apps are built with web technologies, they can run just as well as a Progressive Web App as they can a native app. Not sure what PWAs are? Check out Ionic's PWA Overview for more info.

Making an App a PWA

The two main requirements of a PWA are a Service Worker and a Web Manifest. While it's possible to add both of these to an app manually, the Angular team has an @angular/pwa package that can be used to automate this.

The @angular/pwa package will automatically add a service worker and an app manifest to the app. To add this package to the app, run:

$ ng add @angular/pwa

Once this package has been added run ionic build --prod and the www directory will be ready to deploy as a PWA.

By default, the @angular/pwa package comes with the Angular logo for the app icons. Be sure to update the manifest to use the correct app name and also replace the icons.

If an app is being deployed to other channels such as Cordova or Electron, you can remove the "serviceWorker": true flag from the angular.json file.

The service worker can be generated by running:

$ ionic build --prod --service-worker

Note: Features like Service Workers and many JavaScript APIs (such as geolocation) require the app be hosted in a secure context. When deploying an app through a hosting service, be aware that HTTPS will be required to take full advantage of Service Workers.

Deploying

Firebase

Firebase hosting provides many benefits for Progressive Web Apps, including fast response times thanks to CDNs, HTTPS enabled by default, and support for HTTP2 push.

First, if not already available, create the project in Firebase.

Next, in a Terminal, install the Firebase CLI:

$ npm install -g firebase-tools

With the Firebase CLI installed, run firebase init within your Ionic project. The CLI prompts:

"Which Firebase CLI features do you want to set up for this folder?" Choose "Hosting: Configure and deploy Firebase Hosting sites."

"Select a default Firebase project for this directory:" Choose the project you created on the Firebase website.

"What do you want to use as your public directory?" Enter "www".

Note: Answering these next two questions will ensure that routing, hard reload, and deep linking work in the app:

Configure as a single-page app (rewrite all urls to /index.html)?" Enter "Yes".

"File www/index.html already exists. Overwrite?" Enter "No".

A firebase.json config file is generated, configuring the app for deployment.

The last thing needed is to make sure caching headers are being set correctly. To do this, add a headers snippet to the firebase.json file. The complete firebase.json looks like:

{
  "hosting": {
    "public": "www",
    "ignore": [
      "firebase.json",
      "**/.*",
      "**/node_modules/**"
    ],
    "rewrites": [
      {
        "source": "**",
        "destination": "/index.html"
      }
    ],
    "headers": [
      {
        "source": "/build/app/**",
        "headers": [
          {
            "key": "Cache-Control",
            "value": "public, max-age=31536000"
          }
        ]
      },
      {
        "source": "ngsw-worker.js",
        "headers": [
          {
            "key": "Cache-Control",
            "value": "no-cache"
          }
        ]
      }
    ]
  }
}

For more information about the firebase.json properties, see the Firebase documentation.

Next, build an optimized version of the app by running:

$ ionic build --prod

Last, deploy the app by running:

$ firebase deploy

After this completes, the app will be live.