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Pragmatist’s Guide to Service Worker I am Lyza Danger Gardner I am an Open Web Engineer at Bocoup I can be found at @lyzadanger and https://www.lyza.com Smashing Conference NYC 2017

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Hi! Service Worker

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A Service Worker is a script…

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A Service Worker consists of a script.

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A Service Worker can act as a proxy.

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without service worker…

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Client (Browser) Network index.html ? index.html ! browser requests resources from network…

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Client Network

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Network Client

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Network Client Service Worker

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Client Network

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• Consists of a script (JavaScript file) • Acts as a proxy between client (browser) and network A Service Worker: …and quite a lot more. • It can: • define and handle offline experiences • improve online web performance…

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Who is this presentation for?

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(Yep. There will be JavaScript.)

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But there will also be wretchedly-drawn characters!

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http://bit.ly/sw-smashing-nyc

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• Consists of a script (JavaScript file) • Acts as a proxy between client (browser) and network • It can: • define and handle offline experiences • improve online web performance… A Service Worker: …and quite a lot more. with regards to this…

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Let’s Give it Context.

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Notifications Background Sync Channel Messaging An ecosystem of related APIs

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WebWorker

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• An object created from within a context • Consists of a JavaScript file • The code in that JavaScript file is run in a worker thread • A web worker has a different global context A Web Worker:

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• An object created from within a context • Consists of a JavaScript file • The code in that JavaScript file is run in a worker thread • A web worker has a different global context A Web Worker: ??? ???

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worker browsing context e.g. a browser window showing a document e.g. a ServiceWorker

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ServiceWorkerGlobalScope window (worker) thread (execution) thread

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ServiceWorkerGlobalScope window (worker) thread (execution) thread Channel Messaging, e.g.

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ServiceWorkerGlobalScope window

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This is starting to seem complicated.

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Eeeek! Power and flexibility involves some complexity.

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Service worker is pretty chill.

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async only all HTTPS A couple of across-the-board rules.

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On its way https://jakearchibald.github.io/isserviceworkerready/ …

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No content

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Let’s Do Something Basic.

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Let’s Make a Service Worker that Accomplishes Nothing.

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We’ll create a JavaScript file for a Service Worker that will listen for fetch events and…do nothing for now.

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listen for fetch events fetch

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Service Worker Browser Fetch Event Network listen for fetch events

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self.addEventListener('fetch', event => { // Do something about it }); service-worker.js Adding an event listener for ‘fetch’ events

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That’s seriously it for the moment…

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Registering our Useless Service Worker

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We need to add some JavaScript to a web page to register the Service Worker. //… index.html service-worker.js

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A Service Worker is registered against a scope.

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Is a path or a pattern, relative to the service worker script’s location, you know, e.g.: ./ ./foo ./foo/bar/baz Scope:

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I want to register the service worker located at service-worker.js against the scope ./blog index.html //…

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I want to register the service worker located at service-worker.js against the scope ./blog index.html blog service-worker.js

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if ('serviceWorker' in navigator) { navigator.serviceWorker.register('service-worker.js'); } index.html Register a service worker

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if ('serviceWorker' in navigator) { navigator.serviceWorker.register('service-worker.js'); } index.html detail Feature detection for service worker support

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navigator.serviceWorker …provides an object…including facilities to register, unregister and update service workers, and access the state of service workers and their registrations. Sincerely, The Service Worker Specification [ServiceWorkerContainer]

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.register( ) navigator.serviceWorker scriptURL,options

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if ('serviceWorker' in navigator) { navigator.serviceWorker.register('service-worker.js'); } index.html detail

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Wait a minute: what happened to scope?

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navigator.serviceWorker.register(scriptURL, options) Scope (String) can be passed as second argument

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if ('serviceWorker' in navigator) { navigator.serviceWorker.register('service-worker.js', './'); } code example

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if ('serviceWorker' in navigator) { navigator.serviceWorker.register('service-worker.js'); } index.html detail Default scope is ‘./’

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if ('serviceWorker' in navigator) { navigator.serviceWorker.register('service-worker.js'); } self.addEventListener('fetch', event => { // Do something about it }); index.html detail service-worker.js

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Let’s enhance the uselessness.

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self.addEventListener('fetch', event => { // Do something about it }); service-worker.js

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FetchEvent

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Things in FetchEvent…

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request respondWith(…) FetchEvent object

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Respond with…with…? self.addEventListener('fetch', event => { event.respondWith( ); }); FetchEvent.respondWith(…) service-worker.js

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The fetch API

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Request Response

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fetch( ) Request Response Network fetch a request, then (we hope) get a response

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Response FetchEvent.respondWith( )

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service-worker.js FetchEvent self.addEventListener('fetch', event => { });

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service-worker.js self.addEventListener('fetch', event => { event.respondWith( ); }); FetchEvent.respondWith()

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fetch( ) Request Response

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service-worker.js self.addEventListener('fetch', event => { event.respondWith( fetch(event.request) ); }); FetchEvent.request respondWith the Promise returned by fetch

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Service Worker Browser Fetch Event Network I need ‘./foo.gif’

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JavaScript Promises in 60 seconds

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Promise

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= fetch( ) Promise Request

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Fulfilled Pending

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Rejected Pending

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Pending OR Settled: Fulfilled Settled: Rejected

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No content

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A Service Worker that Does Something!

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We’ll extend our Service Worker so that it shows a custom offline message to a user when they are offline.

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Client Network Online

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Client Network Online

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If you see this, you are online

if ('serviceWorker' in navigator) { navigator.serviceWorker.register('service-worker.js', './'); } index.html

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Network Client Service Worker Offline

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Network Client Service Worker Offline

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self.addEventListener('fetch', event => { event.respondWith( fetch(event.request) ); }); service-worker.js Network The Happy (Online) Path

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fetch( ) Promise Request Response Network The Happy (Online) Path

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fetch( ) Request Offline! Network The Sad (Offline) Path

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fetch( ) Request Offline! Network .catch( ) The Sad (Offline) Path

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event.respondWith( fetch(event.request).catch(error => { // Do something about it }) ); service-worker.js (detail) handle the offline situation in the catch

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Response need a web-page-like Response!

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new Response(body, init)

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event.respondWith( fetch(event.request).catch(error => { return new Response( ); }) ); service-worker.js (detail)

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event.respondWith( fetch(event.request).catch(error => { return new Response('

Oh, dear.

’, ); }) ); service-worker.js (detail)

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service-worker.js (detail) event.respondWith( fetch(event.request).catch(error => { return new Response('

Oh, dear.

', { headers: { 'Content-Type': 'text/html' } }); }) );

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There’s a problem with this.

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Offline: we’re responding to all fetches with a janky web page.

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event.request.mode

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event.request.mode === ‘navigate’

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event.request.method === 'GET' && In browsers that don’t support request.mode

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event.request.method === 'GET' && event.request.headers.get(‘accept').includes('text/html')) In browsers that don’t support request.mode

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self.addEventListener('fetch', event => { if (event.request.mode === 'navigate') { event.respondWith( fetch(request).catch(error => { return new Response('

Oh, dear.

', { headers: { 'Content-Type': 'text/html' } }); }) ); } }); service-worker.js

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index.html service-worker.js self.addEventListener('fetch', event => { if (event.request.mode === 'navigate') { event.respondWith( fetch(request).catch(error => { return new Response('

Oh, dear.

', { headers: { 'Content-Type': 'text/html' } }); }) ); } });

If you see this, you are online

if ('serviceWorker' in navigator) { navigator.serviceWorker.register('service-worker.js', './'); }

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Now we have an offline message.

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We can do better.

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Let’s use our SW to serve an offline page.

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self.addEventListener('fetch', event => { if (event.request.mode === 'navigate') { event.respondWith( fetch(request).catch(error => { return new Response('

Oh, dear.

', { headers: { 'Content-Type': 'text/html' } }); }) ); } }); service-worker.js Let’s not do this…

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Registering a Service Worker

Offline Fallback Test

If you see this, you are offline

offline.html instead, let’s use a real HTML page

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We’ll extend our Service Worker so that it provides a custom offline page when navigation requests are made and the network is unavailable.

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Registering a Service Worker

Offline Fallback Test

If you see this, you are offline

offline.html Gotta stash the offline page first!

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Service Worker lifecycle

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parsed Service Worker state

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parsed installing Service Worker state

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parsed installing installed Service Worker state

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install phase

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self.addEventListener('install', event => { // Stash offline page in a cache }); service-worker.js (detail)

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Install Event

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ExtendableEvent

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ExtendableEvent.waitUntil(promise)

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self.addEventListener('install', event => { event.waitUntil( // ... ); }); service-worker.js (detail)

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The Cache API

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cache

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cache

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cache

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cache offline-items

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cache offline-items

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You have complete control over caches

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CacheStorage caches

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methods ServiceWorkerGlobalScope properties fetch caches

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Caching Offline Page

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.open(‘offline’) caches

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.open(‘offline’) caches

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new Request( ) ‘offline.html’ offline need both a Request and Response to put in cache…

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new Response(body, init) fetch We want the Response to represent the offline.html page…

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self.addEventListener('install', event => { var offlineURL = 'offline.html'; event.waitUntil( ); }); service-worker.js (install event handler detail)

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self.addEventListener('install', event => { var offlineURL = 'offline.html'; event.waitUntil( ); }); service-worker.js (install event handler detail) service-worker.js (install event handler detail)

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self.addEventListener('install', event => { var offlineURL = 'offline.html'; event.waitUntil( fetch(new Request(offlineURL)).then(response => { }) ); }); Step 1 service-worker.js (install event handler detail)

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self.addEventListener('install', event => { var offlineURL = 'offline.html'; event.waitUntil( fetch(new Request(offlineURL)).then(response => { return caches.open('offline').then(cache => { }); }) ); }); Step 2 service-worker.js (install event handler detail)

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cache.put(request, response)

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self.addEventListener('install', event => { var offlineURL = 'offline.html'; event.waitUntil( fetch(new Request(offlineURL)).then(response => { return caches.open('offline').then(cache => { return cache.put(new Request(offlineURL), response); }); }) ); }); Step 3 service-worker.js (install event handler detail)

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offline caches.open( ) fetch( ) cache.put( , ) ‘offline.html’ offline Step 1 Step 2 Step 3

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Serving the offline page.

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self.addEventListener('fetch', event => { if (event.request.mode === 'navigate') { event.respondWith( fetch(request).catch(error => { return new Response('

Oh, dear.

', { headers: { 'Content-Type': 'text/html' } }); }) ); } }); service-worker.js (fetch event handler detail) instead of…

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cache.match(request) find the offline page in cache…

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self.addEventListener('fetch', event => { if (event.request.mode === 'navigate') { event.respondWith( fetch(event.request).catch(error => { return caches.open('offline').then(cache => { }); }) ); } }); service-worker.js (fetch event handler detail)

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self.addEventListener('fetch', event => { if (event.request.mode === 'navigate') { event.respondWith( fetch(event.request).catch(error => { return caches.open('offline').then(cache => { return cache.match('offline.html'); }); }) ); } }); service-worker.js (fetch event handler detail) You can use URL in place of Request here…

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return cache.match(new Request('offline.html')); return cache.match('offline.html'); is same effect as:

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Client Network Online

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Network Client Service Worker Offline

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Network Strategies

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We can make a Service Worker that implements different network strategies for different types of requests.

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HTML network caches 1 2 network-first strategy

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image network caches 1 2 cache-first strategy

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1 2 Determining what kind of request a given fetch represents. Getting stuff into caches so it’s there for later.

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self.addEventListener('fetch', event => { if (event.request.mode === 'navigate') { event.respondWith(/* network-first strategy */); } }); 1 service-worker.js (fetch handler detail)

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self.addEventListener('fetch', event => { if (event.request.mode === 'navigate') { event.respondWith(/* network-first strategy */); } else if (event.request.headers.get('Accept').indexOf('image') !== -1) { event.respondWith(/* cache-first strategy */); } }); 1 service-worker.js (fetch handler detail)

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1 2 Determining what kind of request a given fetch represents. Getting stuff into caches so it’s there for later.

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Network-First Strategy

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Part I: Online Behavior (a.k.a. the “happy path”)

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assets caches.open( ) fetch( ) cache.put( , ) assets network-first strategy Step 1 Step 2 Step 3 Network

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Read-through caching 2 if (event.request.mode === 'navigate') { event.respondWith(fetch(event.request) .then(response => { }) ); } service-worker.js (fetch handler detail)

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Response.ok if (event.request.mode === 'navigate') { event.respondWith(fetch(event.request) .then(response => { if (response.ok) { } }) ); } service-worker.js (fetch handler detail) 2

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Response.clone() if (event.request.mode === 'navigate') { event.respondWith(fetch(event.request) .then(response => { if (response.ok) { caches.open('assets').then(cache => { cache.put(event.request, response.clone()); }); } }) ); } service-worker.js (fetch handler detail) 2

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2 if (event.request.mode === 'navigate') { event.respondWith(fetch(event.request) .then(response => { if (response.ok) { caches.open('assets').then(cache => { cache.put(event.request, response.clone()); }); } return response; }) ); } service-worker.js (fetch handler detail)

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Part II: Offline Behavior (a.k.a. the fallback path)

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caches.match( ) fetch( ) network-first strategy Network

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caches.match( )

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vs. undefined caches.match( ) cache.match( ) when no match found, Promise resolves to undefined

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if (event.request.mode === 'navigate') { event.respondWith(fetch(event.request) .then(response => { if (response.ok) { caches.open('assets').then(cache => { cache.put(event.request, response.clone()); }); } return response; }) ); } service-worker.js (fetch handler detail)

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if (event.request.mode === 'navigate') { event.respondWith(fetch(event.request) .then(response => { }) ); } service-worker.js (fetch handler detail) fold happy path out of the way…

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if (event.request.mode === 'navigate') { event.respondWith(fetch(event.request) .then(response => { }) .catch(() => { }) ); } service-worker.js (fetch handler detail)

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if (event.request.mode === 'navigate') { event.respondWith(fetch(event.request) .then(response => { }) .catch(() => { return caches.match(event.request).then(response => { }); }) ); } service-worker.js (fetch handler detail)

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if (event.request.mode === 'navigate') { event.respondWith(fetch(event.request) .then(response => { }) .catch(() => { return caches.match(event.request).then(response => { if (!response) { throw Error(`${request.url} not found in cache`); } }); }) ); } service-worker.js (fetch handler detail)

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if (event.request.mode === 'navigate') { event.respondWith(fetch(event.request) .then(response => { }) .catch(() => { return caches.match(event.request).then(response => { if (!response) { throw Error(`${request.url} not found in cache`); } return response; }); }) ); } service-worker.js (fetch handler detail)

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Part IIa: Offline Behavior (a.k.a. the fallback fallback path)

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caches.match( ) fetch( ) cache.match( ) offline caches.open(‘offline’) ‘offline.html’

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if (event.request.mode === 'navigate') { event.respondWith(fetch(event.request) .then(response => { }) .catch(() => { return caches.match(event.request).then(response => { if (!response) { throw Error(`${request.url} not found in cache`); } return response; }); }) ); } service-worker.js (fetch handler detail) service-worker.js (fetch handler detail)

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if (event.request.mode === 'navigate') { event.respondWith(fetch(event.request) .then(response => { }) .catch(() => { }) ); } service-worker.js (fetch handler detail) service-worker.js (fetch handler detail)

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if (event.request.mode === 'navigate') { event.respondWith(fetch(event.request) .then(response => { }) .catch(() => { }) .catch(() => { }) ); } service-worker.js (fetch handler detail) service-worker.js (fetch handler detail)

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if (event.request.mode === 'navigate') { event.respondWith(fetch(event.request) .then(response => { }) .catch(() => { }) .catch(() => { return caches.open('offline').then(cache => { return cache.match('offline.html'); }); }) ); } service-worker.js (fetch handler detail) service-worker.js (fetch handler detail)

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caches.match( ) fetch( ) network-first strategy

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caches.match( ) fetch( ) cache-first strategy undefined

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assets caches.open( ) fetch( ) cache.put( , ) assets read-through caching

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cache.put(request, response) cache.add(requestOrURL) “ ”

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cache.addAll(urls) “ ” cache.add(requestOrURL)

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Application Shell

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Need to precache app shell assets during install…

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1 2 Put assets into cache during install phase. Later, respond to fetches for static assets with a cache-first strategy.

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const cacheFiles = [ '', 'default.css', 'static-assets/cloud-1.jpg', 'static-assets/cloud-2.jpg', 'static-assets/cloud-3.jpg', 'static-assets/cloud-4.jpg', 'static-assets/cloud-5.jpg', 'static-assets/cloud-6.jpg', 'static-assets/cloud-7.jpg', 'static-assets/cloud-8.jpg', 'static-assets/cloud-9.jpg', 'static-assets/cloud-10.jpg' ]; service-worker.js (detail) 1

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self.addEventListener('install', event => { event.waitUntil( caches.open('static').then(cache => { }) ); }); service-worker.js (install handler detail) 1

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self.addEventListener('install', event => { event.waitUntil( caches.open('static').then(cache => { return cache.addAll(cacheFiles); }) ); }); 1 service-worker.js (install handler detail)

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self.addEventListener('fetch', event => { var url = new URL(event.request.url); if (cacheFiles.indexOf(url.pathname) !== -1) { event.respondWith( ); } }); 2 service-worker.js (fetch handler detail) responding to fetch events for app shell assets

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self.addEventListener('fetch', event => { var url = new URL(event.request.url); if (cacheFiles.indexOf(url.pathname) !== -1) { event.respondWith( caches.match(event.request).then(response => { if (!response) { throw Error(`${event.request.url} not found in cache`); } return response; }) ); } }); 2 service-worker.js (fetch handler detail)

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self.addEventListener('fetch', event => { var url = new URL(event.request.url); if (cacheFiles.indexOf(url.pathname) !== -1) { event.respondWith( caches.match(event.request).then(response => { if (!response) { throw Error(`${event.request.url} not found in cache`); } return response; }).catch(() => fetch(event.request)) ); } }); 2 service-worker.js (fetch handler detail)

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Service Worker state parsed installing installed

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parsed installing installed Service Worker state activating

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parsed installing installed Service Worker state activating activated

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service-worker.js (NEW!) parsed installing installed activating activated

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service-worker.js (NEW!) parsed installing installed activating activated

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service-worker.js (NEW!) parsed installing installed activating activated

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service-worker.js (NEW!) parsed installing installed activating activated

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service-worker.js (NEW!) parsed installing installed activating activated

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parsed installing installed activating activated service-worker.js (NEW!) ?

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parsed installing installed activating activated service-worker.js (NEW!) X If no previous SW, activation starts automatically

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parsed installing installed activating activated service-worker.js (NEW!) X

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parsed installing installed activating activated service-worker.js (NEW!) X

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parsed installing installed activating activated service-worker.js (NEW!)

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parsed installing installed activating activated service-worker.js (NEW!) ?

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parsed installing installed activating activated service-worker.js (NEW!) ! If previous SW, activation does not happen until…

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service-worker.js (NEW!) (waiting)

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service-worker.js (NEW!) (waiting) All controlled clients close…

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self.addEventListener('install', event => { event.waitUntil( caches.open('static').then(cache => { return cache.addAll(cacheFiles); }) ); }); service-worker.js (install handler detail)

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self.addEventListener('install', event => { event.waitUntil( caches.open('static').then(cache => { return cache.addAll(cacheFiles); }).then(() => self.skipWaiting()) ); }); service-worker.js (install handler detail) Make SW activate immediately

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methods ServiceWorkerGlobalScope properties fetch caches skipWaiting

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Versioning a Service Worker

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cleaning up after old SW caches and versions

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No content

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activate event

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ExtendableEvent

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self.addEventListener('activate', event => { event.waitUntil( // Clean up after old service worker versions ); });

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const cachePrefix = 'thisIsMyVersion'; Update the version string each time you change the service worker

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Use the prefix caches.open(`${cachePrefix}-static`)

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[ ] , , caches.keys()

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self.addEventListener('activate', event => { event.waitUntil( caches.keys().then(cacheKeys => { }) ); }); service-worker.js (activate handler detail)

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self.addEventListener('activate', event => { event.waitUntil( caches.keys().then(cacheKeys => { var oldCacheKeys = cacheKeys.filter(key => { return (key.indexOf(cachePrefix) !== 0); }); }) ); }); service-worker.js (activate handler detail) Array.prototype.filter

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self.addEventListener('activate', event => { event.waitUntil( caches.keys().then(cacheKeys => { var oldCacheKeys = cacheKeys.filter(key => { return (key.indexOf(cachePrefix) !== 0); }); var deletePromises = oldCacheKeys.map(oldKey => { return caches.delete(oldKey); }); }) ); }); Array.prototype.map service-worker.js (activate handler detail)

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self.addEventListener('activate', event => { event.waitUntil( caches.keys().then(cacheKeys => { var oldCacheKeys = cacheKeys.filter(key => { return (key.indexOf(cachePrefix) !== 0); }); var deletePromises = oldCacheKeys.map(oldKey => { return caches.delete(oldKey); }); return Promise.all(deletePromises); }) ); }); service-worker.js (activate handler detail)

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methods ServiceWorkerGlobalScope properties fetch caches skipWaiting clients

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clients.claim()

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self.addEventListener('activate', event => { event.waitUntil( caches.keys().then(cacheKeys => { var oldCacheKeys = cacheKeys.filter(key => { return (key.indexOf(cachePrefix) !== 0); }); var deletePromises = oldCacheKeys.map(oldKey => { return caches.delete(oldKey); }); return Promise.all(deletePromises); }).then(() => self.clients.claim()) ); }); Make SW take control immediately

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That’s it for today

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But that’s not all!

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bit.ly/sw-smashing-nyc

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• Recipes for: • creating an offline image • Using an external JSON file for managing application shell asset URLs • Links to resources and documentation Repository also includes:

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Pragmatist’s Guide to Service Worker I am Lyza Danger Gardner I am an Open Web Engineer at Bocoup I can be found at @lyzadanger and https://www.lyza.com Smashing Conference NYC 2017 http://bit.ly/sw-smashing-nyc