Maxim Salnikov

@webmaxru

Diving deep, deep offline –

the web can do it!

What is an offline-ready web application

And how to build it today

Maxim Salnikov

@webmaxru

PWA Slack organizer
PWA Oslo / PWA London meetups organizer
PWA speaker and trainer
Google Dev Expert in Web Technologies

Azure Developer Technical Lead at Microsoft

The World Wide Web is the New Software Platform
The Web Browser is the New Operating System
JavaScript is the de facto Programming Language of the Web

Web Browser as an Application Platform: The Lively Kernel Experience

Antero Taivalsaari, Tommi Mikkonen, Dan Ingalls, Krzysztof Palacz

January, 2008

Web as an app platform is amazing

Browsers

Almost on every device with UI
Evergreen
APIs to access device hardware

Web as an app platform is amazing

JavaScript

Browsers

Versatile language
Powerful tooling
Evolving in a smart way

Web as an app platform is amazing

JavaScript

JS Engines

Browsers

Focus on the performance
Embedding possibilities

Web as an app platform is amazing

JavaScript

JS Engines

UI Layer

Browsers

Convenient tools to build responsive UIs
Focus on accessibility
Variety of high-quality components and libraries

Web as an app platform is amazing

Community

JavaScript

JS Engines

UI Layer

Browsers

https://insights.stackoverflow.com/survey/2019

69.7%

Web as an app platform is amazing

Community

JavaScript

JS Engines

UI Layer

Browsers

Issues?

Historically depends on the "connection status"

Solutions

Caching

Installing

HTTP Cache?
AppCache

Save page as... (complete)
Chrome Apps
Electron
NativeScript, React Native

What is PWA at all?

Progressive web apps use modern web APIs along with traditional progressive enhancement strategy to create cross-platform web applications.

https://developer.mozilla.org/en-US/Apps/Progressive

These apps work everywhere and provide several features that give them the same user experience advantages as native apps.

works everywhere*

* but not everything**

natively

** use progressive enhancement strategy

Offline-

ready

<

>

=

https://developers.google.com/web/updates/2019/06/pwa-install-addressbar

Installation as a native app

Proper offline-ready web app

App itself
Online runtime data
Offline runtime data
Connection failures
Updates
Platform features

Always available
Thoughtfully collected
Safely preserved
Do not break the flow
Both explicit and implicit
For the win!

While keeping its web nature!

Application UI

Let's build an App shell

My App

Define assets
Put in the cache
Serve from the cache
Manage versions

}

Service worker

Logically

Physically

-file(s)

App

Service worker

Browser/OS

Event-driven worker

Cache

fetch

push

sync

Managing the cache

self.addEventListener('install', event => {
  
    // Use Cache API to cache html/js/css

})

self.addEventListener('activate', event => {
  
    // Clean the cache from the obsolete versions

})

handmade-service-worker.js

In the real world

Can't add opaque responses directly
Redirected requests should be managed
Always creating a new version of cache and deleting the old one is not optimal
Control over cache size is required
Cache invalidation for runtime caching is complex
...

Serving from the cache

self.addEventListener('fetch', event => {

  if (event.request.url.indexOf('/api') != -1) {
    event.respondWith(
      // Network-First Strategy (for API?)
    )
  } else {
    event.respondWith(
      // Cache-First Strategy (for app shell?)
    )
  }
})

handmade-service-worker.js

In the real world

All kinds of fallbacks needed for the strategies
There are more complex strategies like Stale-While-Revalidate
Good to have some form of the routing
Good to have the possibility to provide some extra settings for different resource groups
...

https://developers.google.com/web/tools/workbox/

Define assets
Put in the cache
Serve from the cache
Manage versions

}

Is there a helper?

# Installing the Workbox Node module
$ npm install workbox-build --save-dev

Configuration

// Sample configuration with the basic options
var workboxConfig = {
  globDirectory: 'dist/',
  globPatterns: [
    '**/*.{txt,png,ico,html,js,json,css}'
  ],
  swSrc: 'src/workbox-service-worker.js',
  swDest: 'dist/sw.js'
}

workbox-build.js

Source service worker

// Importing Workbox itself from Google CDN
importScripts('https://googleapis.com/.../workbox-sw.js');

// Precaching and setting up the routing
workbox.precaching.precacheAndRoute([])

src/workbox-service-worker.js

Caching, serving, managing versions

Build service worker

// We will use injectManifest mode
const {injectManifest} = require('workbox-build')

// Sample configuration with the basic options
var workboxConfig = {...}

// Calling the method and output the result
injectManifest(workboxConfig).then(({count, size}) => {
    console.log(`Generated ${workboxConfig.swDest},
    which will precache ${count} files, ${size} bytes.`)
})

workbox-build.js

Build flow integration

{
  "scripts": {
    "build-pwa": "npm run build-app &&
                  node workbox-build.js"
  }
}

package.json

Runtime application data

Intercepting requests

self.addEventListener('fetch', event => {

  if (event.request.url.indexOf('/api/breakingnews') != -1) {
    event.respondWith(
      // Network-First Strategy
    )
  } else if (event.request.url.indexOf('/api/archive') != -1 {
    event.respondWith(
      // Cache-First Strategy
    )
  }
})

handmade-service-worker.js

Routes and strategies

workbox.routing.registerRoute(
  new RegExp('/api/breakingnews'),
  new workbox.strategies.NetworkFirst()
);

src/workbox-service-worker.js

workbox.routing.registerRoute(
  new RegExp('/api/archive'),
  new workbox.strategies.CacheFirst({
    plugins: [...]
  })
);

Strategies

CacheFirst
CacheOnly
NetworkFirst
NetworkOnly
StaleWhileRevalidate

Plugins

Expiration
CacheableResponse
BroadcastUpdate
BackgroundSync
...your own plugin?

Save and sync offline actions

Background sync

One-off event for offline -> online
No active app tab required

https://developers.google.com/web/updates/2015/12/background-sync

navigator.serviceWorker.ready.then( swRegistration => {
  return swRegistration.sync.register('postTweet');
});

main.js

self.addEventListener('sync', event => {
  if (event.tag == 'postTweet') {
    event.waitUntil(
        // Do useful things...
    );
  }
});

handmade-service-worker.js

const postTweetPlugin =
    new workbox.backgroundSync.Plugin('tweetsQueue', {
        maxRetentionTime: 24 * 60 // Max retry period
    })

src/workbox-service-worker.js

workbox.routing.registerRoute(
  /(http[s]?:\/\/)?([^\/\s]+\/)post-tweet/,
  new workbox.strategies.NetworkOnly({
    plugins: [postTweetPlugin]
  }),
  'POST'
)

https://developers.google.com/web/tools/workbox/modules/workbox-background-sync

Full control over downloads

Background fetch

Pause/resume download/upload automatically
Aware of fetch status/progress
No need to keep the app open
UI for the user to pause/cancel and track progress

https://developers.google.com/web/updates/2018/12/background-fetch

const registration = await navigator.serviceWorker.ready;
await registration.backgroundFetch.fetch(
  'my-series',
  ['s01e01.mpg', 's01e02.mpg'],
  {
    title: 'Downloading My Series',
    downloadTotal: 600 * 1024 * 1024
   }
);

main.js

addEventListener('backgroundfetchsuccess', event => {
  event.waitUntil(
    (async function() {
      try {
        // Put the responses to Cache Storage
        ...
        await event.updateUI({ title: `Downloaded!` });
      } catch (err) {
        await event.updateUI({ title: `Fail: ${err}` });
      }
    })()
  );
});

src/service-worker.js

More details

https://medium.com/@webmaxru/background-fetch-api-get-ready-to-use-it-69cca522cd8f

Schedule your updates

https://developers.google.com/web/updates/2019/08/periodic-background-sync

Periodic background sync

Like a "Cron" in the browser
Connection independent
Cadence set by the developer

Another API for that
Works only online
Browser decides

const registration = await navigator.serviceWorker.ready;
if ('periodicSync' in registration) {
  try {
    registration.periodicSync.register('refreshTweets', {
      // An interval of one day.
      minInterval: 24 * 60 * 60 * 1000,
    });
  } catch (error) {
    // PBS cannot be used.
  }
}

main.js

self.addEventListener('periodicsync', (event) => {
  if (event.tag === 'refreshTweets') { 
    event.waitUntil(
    	// [Maybe] Do the job
    );
  }
});

src/service-worker.js

Network connection type?
Data saver mode?
Available storage space?

Full-fledged application platform
Offline-ready mechanisms are in production
Awesome tools are available
User experience & security is the key

And this is just the beginning!

Web platform today

Thank you!

Maxim Salnikov

@webmaxru

bit.ly/go-pwa-slack

2000+ developers
Major browsers/frameworks/libs reps

t.me/pwa_ru

Все о PWA на русском языке

chrome://flags/#enable-devtools-experim

Debugging background services

More platform tools

https://developers.google.com/web/updates/2019/08/native-file-system

Native File System API

https://developers.google.com/web/updates/2018/12/badging-api

Badging API

https://developers.google.com/web/updates/2019/08/contact-picker

Contact Picker API

Features flying soon

https://goo.gle/fugu-api-tracker

Almost 100 new APIs

Full-fledged application platform
Offline-ready mechanisms are in production
Awesome tools are available
User experience & security is the key

And this is just the beginning!

Web platform today

bit.ly/go-pwa-slack

2000+ developers
Major browsers/frameworks/libs reps

t.me/pwa_ru

Все о PWA на русском языке

Thank you!

Maxim Salnikov

@webmaxru

Questions?

Maxim Salnikov

@webmaxru

Diving deep, deep offline — the web can do it

By Maxim Salnikov

Diving deep, deep offline — the web can do it

There is no need to advocate for progressive web apps anymore. The idea of connection-independent applications has proven its viability and we see many projects following that path, making the offline-ready behavior a best practice, good manner of the web. In my session, based on the exploration of Service Worker API (Cache Storage, Background Fetch, Background Sync) we go through the history of the offline web, treating the network as an enhancement, current challenges, solutions, and proper tooling.

3,806

Diving deep, deep offline –

the web can do it!

What is an offline-ready web application

And how to build it today

Maxim Salnikov

@webmaxru

PWA Slack organizer

PWA Oslo / PWA London meetups organizer

PWA speaker and trainer

Google Dev Expert in Web Technologies

The World Wide Web is the New Software Platform

The Web Browser is the New Operating System

JavaScript is the de facto Programming Language of the Web

January, 2008

Web as an app platform is amazing

Almost on every device with UI

Evergreen

APIs to access device hardware

Web as an app platform is amazing

Versatile language

Powerful tooling

Evolving in a smart way

Web as an app platform is amazing

Focus on the performance

Embedding possibilities

Web as an app platform is amazing

Convenient tools to build responsive UIs

Focus on accessibility

Variety of high-quality components and libraries

Web as an app platform is amazing

69.7%

Web as an app platform is amazing

Historically depends on the "connection status"

Solutions

Caching

Installing

HTTP Cache?

AppCache

Save page as... (complete)

Chrome Apps

Electron

NativeScript, React Native

What is PWA at all?

These apps work everywhere and provide several features that give them the same user experience advantages as native apps.

works everywhere*

natively

Offline-

ready

<

>

=

Installation as a native app

Proper offline-ready web app

App itself

Online runtime data

Offline runtime data

Connection failures

Updates

Platform features

Always available

Thoughtfully collected

Safely preserved

Do not break the flow

Both explicit and implicit

For the win!

While keeping its web nature!

Application UI

Let's build an App shell

Define assets

Put in the cache

Serve from the cache

Manage versions

}

Service worker

Logically

Physically

-file(s)

Managing the cache

handmade-service-worker.js

In the real world