PWA Deep Dive: Offlineanwendungen im Griff

Zentrale Eigenschaft jeder Progressive Web App (PWA) ist die Verbindungsunabhängigkeit. Dank dem Service Worker funktioniert die App auch dann, wenn der Anwender gerade offline ist: im Tunnel, im Park oder im Dschungel. Bei der Generierung eines Service Workers hilft das Toolkit Workbox. Anwenderdaten werden hingegen in der Browserdatenbank IndexedDB hinterlegt. Wo Daten offline gehalten werden, müssen aber auch deren Synchronisierung und Konfliktauflösung in der Architektur bedacht werden. Christian Liebel zeigt Ihnen die Mechanik hinter dem Service-Worker-Cache und der Browserdatenbank IndexedDB, sodass es auch Ihre PWA mit den nativen Gegenstücken problemlos aufnehmen kann.

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1. PWA Deep Dive Offlineanwendungen im Griff Christian Liebel @christianliebel Consultant
2. PWA Deep Dive Offlineanwendungen im Griff Responsive Linkable Discoverable Installable App-like Connectivity Independent Fresh Safe Re-engageable Progressive
3. PWA Deep Dive Offlineanwendungen im Griff
4. Service Worker & Cache API Source Files & Assets App & IndexedDB Structured Data PWA Deep Dive Offlineanwendungen im Griff Connectivity Independent
5. Offline First Service Worker Cache API Workbox Angular Demo App IndexedDB Dexie.js Dexie.js Migrations PWA Deep Dive Offlineanwendungen im Griff Talking Points
6. Offline First Service Worker Cache API Workbox Angular Demo App IndexedDB Dexie.js Dexie.js Migrations PWA Deep Dive Offlineanwendungen im Griff Talking Points
7. Offline Capability Challenge: Connection strength varies a lot (especially en route) Lie-Fi: Connection strength of a public WiFi is weak or even completely offline Goal: App works offline or with a weak connection at least within the possibilities (e.g. OneNote) PWA Deep Dive Offlineanwendungen im Griff Offline First
8. Principle PWA Deep Dive Offlineanwendungen im Griff Offline First - Draft and implement offline support first - Think about synchronization & conflicts - Don’t treat offline as an error - Make offline the default - Everything must be offline capable
9. PWA Deep Dive Offlineanwendungen im Griff Offline First System Website HTML/JS Local storage Central adapter Remote storage Server Internet
10. Locking Pessimistic - System locks access to resource if it is used by another user - No conflicts - Users don’t like this (offline = no locking possible!) Optimistic - Users can access arbitrary resources anytime - Requires data synchronization & conflict resolution (strategies depend on domain) PWA Deep Dive Offlineanwendungen im Griff Offline First
11. Offline First Service Worker Cache API Workbox Angular Demo App IndexedDB Dexie.js Dexie.js Migrations PWA Deep Dive Offlineanwendungen im Griff Talking Points
12. Key Technology Service Worker Service Worker Internet Website HTML/JS Cache fetch Offlineanwendungen im Griff PWA Deep Dive
13. Worker snippet is executed in an own thread Worker can’t manipulate the parent document’s DOM Communication via thin API (postMessage) Acts as a controller/proxy/interceptor Performs background tasks Has to be installed before usage Relation: Scope (origin + path) Lifetime: Unrelated to tab/window PWA Deep Dive Offlineanwendungen im Griff Service Worker
14. Lifecycle PWA Deep Dive Offlineanwendungen im Griff Service Worker Installing Parsed Error Activated Idle Terminated fetch/ message
15. Platform Support Service Worker Offlineanwendungen im Griff PWA Deep Dive 17 11.1 44 40 4.1 Chrome 40 11.3
16. Basic Implementation navigator.serviceWorker.register('sw.js') .then(subscription => console.log(subscription)) .catch(err => console.error('Fehler', err)); self.addEventListener('install', event => {}); self.addEventListener('activate', () => {}); self.addEventListener('fetch', event => {}); PWA Deep Dive Offlineanwendungen im Griff Service Worker LIVE DEMO
17. Debugging PWA Deep Dive Offlineanwendungen im Griff Service Worker
18. Offline First Service Worker Cache API Workbox Angular Demo App IndexedDB Dexie.js Dexie.js Migrations PWA Deep Dive Offlineanwendungen im Griff Talking Points
19. Introduction Cache: Key-value storage Key: HTTP(S) request, value: HTTP(S) response Survives browser restarts (Safari: unused caches are cleared “after a few weeks”) Can be accessed from both service worker and website Isolated per origin (protocol + hostname + port) Multiple named caches per origin Cache operations are asynchronous (Promises) PWA Deep Dive Offlineanwendungen im Griff Cache API
20. Usage 1. Open a cache 2. Store/read responses from the cache PWA Deep Dive Offlineanwendungen im Griff Cache API await caches.open('images') await cache.put(req, res) await cache.add(req) await cache.match(req)
21. and Service Worker PWA Deep Dive Offlineanwendungen im Griff Cache API Installing Parsed Error Activated Idle Terminated fetch/ message Install cache content Remove old caches Deliver from cache
22. Adding Requests to The Cache self.addEventListener('install', event => { event.waitUntil( caches.open('pwa-demo-v1') .then(cache => cache.addAll(['/', '/index.html'])) .then(() => self.skipWaiting()) ); }); PWA Deep Dive Offlineanwendungen im Griff Cache API LIVE DEMO
23. Delivering from The Cache self.addEventListener('fetch', event => { event.respondWith( caches.match(event.request) .then(response => response || fetch(event.request)) ); }); PWA Deep Dive Offlineanwendungen im Griff Cache API LIVE DEMO
24. Debugging PWA Deep Dive Offlineanwendungen im Griff Cache API
25. Caching Strategies 1. Cache only 2. Network only 3. Cache falling back to network 4. Cache & network race 5. Network falling back to cache 6. Cache then network 7. Generic Fallback 8. Service-Worker-side templating PWA Deep Dive Offlineanwendungen im Griff Cache API https://jakearchibald.com/2014/offline-cookbook/
26. Use Cases Service Worker - everything that’s part of a website/app version - application source files - assets Application - dynamic content known during runtime - “read later”, profile images, … - lookup without fetch PWA Deep Dive Offlineanwendungen im Griff Cache API
27. Offline First Service Worker Cache API Workbox Angular Demo App IndexedDB Dexie.js Dexie.js Migrations PWA Deep Dive Offlineanwendungen im Griff Talking Points
28. Overview Toolchain by Google: Service Worker generator and runtime library Automatically creates a Service Worker implementation for you Can extend an existing Service Worker implementation with caching Command line tool: workbox npm i -g workbox-cli PWA Deep Dive Offlineanwendungen im Griff Workbox
29. Commands workbox wizard workbox generateSW workbox injectManifest PWA Deep Dive Offlineanwendungen im Griff Workbox LIVE DEMO
30. Offline First Service Worker Cache API Workbox Angular Demo App IndexedDB Dexie.js Dexie.js Migrations PWA Deep Dive Offlineanwendungen im Griff Talking Points
31. PWA Setup Angular supports service worker and cache manifest generation (for productive builds only) npm i -g @angular/cli ng new myApp cd myApp ng add @angular/pwa ng build --prod PWA Deep Dive Offlineanwendungen im Griff Angular LIVE DEMO
32. Update Process PWA Deep Dive Offlineanwendungen im Griff Angular V1 V2 V2 V1 V1 V2 Server Browser
33. SwUpdate The SwUpdate service provides an available observable that fires when there’s an update. As a result, the user can be prompted to reload the website. PWA Deep Dive Offlineanwendungen im Griff Angular
34. Offline First Service Worker Cache API Workbox Angular Demo App IndexedDB Dexie.js Dexie.js Migrations PWA Deep Dive Offlineanwendungen im Griff Talking Points
35. Motivation The web platform has different techniques to store arbitrary data (e.g. application state) offline: • Web Storage API (Local Storage/Session Storage—synchronous!) • Cookies (inconvenient) • IndexedDB PWA Deep Dive Offlineanwendungen im Griff IndexedDB
36. Overview Indexed Database (IndexedDB) is a database in the browser capable of storing structured data in tables with keys and value Data is stored permanently (survives browser restarts) Service Worker and website share access to the same IndexedDB database (e.g. for synchronization purposes) PWA Deep Dive Offlineanwendungen im Griff IndexedDB
37. Browser Support PWA Deep Dive Offlineanwendungen im Griff IndexedDB 10 7.1 4 11
38. Offline First Service Worker Cache API Workbox Angular Demo App IndexedDB Dexie.js Dexie.js Migrations PWA Deep Dive Offlineanwendungen im Griff Talking Points
39. Overview Dexie is a minimalistic wrapper for IndexedDB Operations are based on promises instead of callbacks Near native performance (also for bulk inserts) Open-source PWA Deep Dive Offlineanwendungen im Griff Dexie.js
40. Table API const table = db.table('todos'); table.toArray() // get all items as an array table.add() // insert an object table.put() // update or insert an object table.filter(i => i.id !== 3) // apply JS filter on value table.where({ name: 'Peter' }) // query items by key PWA Deep Dive Offlineanwendungen im Griff Dexie.js
41. …and TypeScript class MyAppDatabase extends Dexie { todos: Dexie.Table<Todo, number>; constructor () { super('MyTodoDatabase'); this.version(1).stores({ todos: '++id', }); this.todos = this.table('todos'); } } PWA Deep Dive Offlineanwendungen im Griff Dexie.js LIVE DEMO
42. IndexedDB Debugging PWA Deep Dive Offlineanwendungen im Griff Dexie.js
43. Offline First Service Worker Cache API Workbox Angular Demo App IndexedDB Dexie.js Dexie.js Migrations PWA Deep Dive Offlineanwendungen im Griff Talking Points
44. Migrations db.version(1).stores({ friends: "++id,name,age" }); db.version(2).stores({ friends: "++id,name,birthdate" }).upgrade(trans => { const YEAR = 365 * 24 * 60 * 60 * 1000; return trans.friends.toCollection().modify(friend => { friend.birthdate = new Date(Date.now() - (friend.age * YEAR)); delete friend.age; }); }); PWA Deep Dive Offlineanwendungen im Griff Dexie.js
45. Make use of the Offline First pattern Use Cache API for HTTPS requests Use IndexedDB for structured data Use Service Workers for initial caching and delivering cached content Think about data synchronization & conflict handling for structured data Make your users happy! PWA Deep Dive Offlineanwendungen im Griff Summary
46. Thank you! Off next: Q&A Christian Liebel @christianliebel christian.liebel@thinktecture.com