PWA Primer

Introduction and mindset presentation for writing PWA applications.

by Gion Kunz

What is PWA?

PWA is the future!

Who is using PWA?

  • Twitter Lite
  • Starbucks
  • Uber
  • Pinterest
  • Spotify
  • many more...
  • Progressive - Work for every user, regardless of browser choice because they’re built with progressive enhancement as a core tenet.
  • Responsive - Fit any form factor, desktop, mobile, tablet, or whatever is next.
  • Connectivity independent - Enhanced with service workers to work offline or on low quality networks.
  • App-like - Use the app-shell model to provide app-style navigations and interactions.
  • Fresh - Always up-to-date thanks to the service worker update process.
  • Safe - Served via TLS to prevent snooping and ensure content hasn’t been tampered with.
  • Discoverable - Are identifiable as “applications” thanks to W3C manifests and service worker registration scope allowing search engines to find them.
  • Re-engageable - Make re-engagement easy through features like push notifications.
  • Installable - Allow users to “keep” apps they find most useful on their home screen without the hassle of an app store.
  • Linkable - Easily share via URL and not require complex installation.


How much PWA?


  • Service Workers - Offline capabilities and updates
  • Web App Manifest - Application Meta Data
  • Cache API - Allows fast caching of HTTP Responses
  • IndexedDB - Client side storage for content
  • Notification API - Native system notifications
  • Push API - Receive server messages
  • Background Sync - Service workers sync in background

Service Workers

caniuse, July 2020, global 1%

  • Intercepts HTTP requests
  • Allows to cache responses 
  • Life-cycle Management
  • Runs in a different Thread than UI
  • Supports Push API* and Background Sync*

* In some browsers ;-)

  .register('/sw.js', { scope: '/sw-example/' })
  .then(reg => {
    // Registration succeeded
  }).catch(error => {
    // Error
// Install phase
self.addEventListener('install', event => {
  event.waitUntil('v1').then(cache => {
      return cache.addAll([
// Fetch interception proxy, try cache, load and cache on miss
self.addEventListener('fetch', event => {
      .then(response => {
        return response ||
          fetch(event.request).then(response => {
  'v1').then(cache =>
              cache.put(event.request, response.clone());
            return response;

Service worker Cache is Fast... REEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEALLY fast......

Twitter Lite Case Study

  • 65% increase in pages per session
  • 75% increase in Tweets sent
  • 20% decrease in bounce rate

Cache for SPeed, Cache for Offline!

Web App Manifest

caniuse, August 2018

  • Allows to specify meta-data which can be used by the OS
  • App specific settings (icons, title, links to app store etc.)
  "name": "HackerWeb",
  "short_name": "HackerWeb",
  "start_url": ".",
  "display": "standalone",
  "background_color" : "#fff" ,
  "description": "Simple HackerNews Web App.",
  "Icons": [{
    "src": "images/touch/homescreen48.png",
    "sizes": "48x48",
    "type": "image/png"

Microsoft Store auto discovery using Bing

  • A non-empty web app manifest file, with at minimum:
    • Name
    • Description
    • App icon icon that is at least 512 x 512 pixels
  • Unique core logic (not minimally modified code from an app boilerplate template)
  • To be served over a secure connection (HTTPS)
  • Service worker script(s)
  • To not violate any laws or Microsoft Store policies.

Background Sync

caniuse, July 2020, gloabl 1%

  • Keeps service worker running until connection is stable 
  • Executes callback which allows to store updates on server
  • Use the Notification API to notify user about progress

Add To Home Screen

caniuse, July 2020, gloabl 1%

  • Allows users to "install" a PWA to their OS
  • Extended reach and lower barrier to entry

Add to home screen in Chrome for Windows!

Best practices and patterns

PRPL is a pattern for structuring and serving Progressive Web Apps (PWAs), with an emphasis on the performance of app delivery and launch.


  • Push critical resources for the initial URL route.
  • Render initial route.
  • Pre-cache remaining routes.
  • Lazy-load and create remaining routes on demand.

Service Worker Patterns

PWA needs proper design

  • What can be done offline and what not?
  • How do we guide the user through offline capabilities?
  • How do we solve synchronization issues?
  • How do we update old clients (and reeeeeeeally old clients)

Angular and PWA

  • CLI can manage your service worker including updates and automatic asset caching
  • CLI creates App Manifest
  • Perfectly matches the PRPL pattern
  • Build your App Shell in the index.html or use Server Side Rendering

Create a PWA Angular app

npm install -g @angular/cli
ng new example-pwa
cd example-pwa
ng add @angular/pwa

Follow PRPL Pattern with Lazy Loading and preload

@NgModule ({
  bootstrap: [AppComponent],
  imports: [
    RouterModule.forRoot(ROUTES, {
      preloadingStrategy: PreloadAllModules
class MainModule {}


  • PWA is the future!
  • PWA is not a framework!
  • PWA is a set of concepts and best-practices supported by various web standards
  • Progressive enhancement and feature detection with graceful fallbacks
  • PWA technology support is getting better and better
  • Include PWA as a core concept at the earliest point in the project possible (analysis and design)

Let's create together.