Advanced Patterns And Strategies

Majid Hajian

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Reliable

Fast

Engaging

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Agenda

  • Background Sync
  • Adaptive Loading
  • Advanced Caching
  • Stream

ME.


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        location: "Oslo, Norway",
        description: '''
        	Passionate Software engineer, 
	        Community Leader, Author and international Speaker
         ''',
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        homepage: "https://www.majidhajian.com",
        socials: {
          twitter: "https://www.twitter.com/mhadaily",
          github: "https://www.github.com/mhadaily"
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        author: {
          Pluralsight: "www.pluralsight.com/authors/majid-hajian",
          Apress: "Progressive Web App with Angular, Book",
          PacktPub: "PWA development, 7 hours video course",
          Udemy: "PWA development, 7 hours video course",
        }
        founder: "Softiware As (www.Softiware.com)"
        devDependencies: {
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Find me on the internet by

Cache API

XHR vs. Fetch API

let xhr = new XMLHttpRequest();
xhr.open('GET', 'http://domain/service');

// request state change event
xhr.onreadystatechange = function() {

  // request completed?
  if (xhr.readyState !== 4) return;

  if (xhr.status === 200) {
    // request successful - show response
    console.log(xhr.responseText);
  }
  else {
    // request error
  }
};

// start request
xhr.send();
fetch(
    'http://domain/service',
    { method: 'GET' }
  )
  .then( response => response.json() )
  .then( json => console.log(json) )
  .catch( error => console.error('error:', error) );

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Cache API

Service Worker

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self.addEventListener('fetch', (event) => {
  console.log('[SW] Fetch ....');
  const request = event.request;
  event.respondWith()
}

FETCH EVENT

Service worker

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event.respondWith(
	caches.match(request)
);

Cache only

Service worker

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event.respondWith(
	fetch(event.request)
);

Network only

Service worker

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event.respondWith(
  caches.match(request).then( (res) => {
    return res || fetch(request).then( (newRes) => {
        caches.open(DYNAMIC_CACHE_VERSION)
        .then( cache => cache.put(request, newRes) );
      return newRes.clone();
    });
  })
);

Cache first, falling back to the network

Service worker

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event.respondWith(
  fetch(request)
    .then((res) => {
      caches.open(DYNAMIC_CACHE_VERSION)
  	    .then(cache => cache.put(request, res));
      return res.clone();
    }) // Fallback to cache
  .catch(err => caches.match(request))
);

The network first, falling back to the cache

Service worker

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event.respondWith(
caches
    .match(request).then((res) => {
      const updatedResopnse = fetch(request)
      	.then((newRes) => {
    	  cache.put(request, newRes.clone());
      return newRes;
    });
   return res || updatedResopnse;
  })
);

Cache with Network Update

Service worker

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const promiseRace = new Promise((resolve, reject) => {
  let firstRejectionReceived = false;
    const rejectOnce = () => {
      if (firstRejectionReceived) {
        reject('No response received.');
      } else {
        firstRejectionReceived = true;
      }
    };
    fetch(request)
        .then(res => res.ok ? resolve(res) : rejectOnce())
        .catch(rejectOnce);
      caches.match(request)
        .then(res => res ? resolve(res) : rejectOnce())
        .catch(rejectOnce);
    });
event.respondWith(promiseRace);

Cache & Network Race

Service worker

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Background Sync

API

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workbox.routing.registerRoute(
  new RegExp('^https:\/\/my-api-server/post\/'),
  workbox.strategies.networkOnly({
    plugins: [bgSyncPlugin]
  }),
  'POST'
)

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const bgSyncPlugin = new workbox.backgroundSync.Plugin('myQueueName', {
  maxRetentionTime: 24 * 60 // Retry for max of 24 Hours
  onSync: async((queue)=>{
    let entry;
  
  	while ((entery = await queue.shiftRequest())){
      
         try {
           // Perform fetch request and perhaps show notificaiton to user 
           // you can also update cache 

         } catch(error) {
           // remove request from the queue
         
         }
      	
    }
  
  });
});

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const showNotification = () => {
  self.registration.showNotification('Post Sent', {
    body: 'You are back online and your post was successfully sent!',
    icon: 'assets/icon/256.png',
    badge: 'assets/icon/32png.png'
  });
};

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Loading based on connectivity speed

adaptiveLoading

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navigator.connection.effectiveType

2G

3G

4G

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2G

3G

4G

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workbox.routing.registerRoute(
  new RegExp('/img/'),
  workbox.strategies.cacheFirst({
    cacheName: 'images',
    plugins: [
      adaptiveLoadingPlugin,
      workbox.expiration.Plugin({
        maxEntries: 50,
        purgeOnQuotaError: true,
      }),
    ],
  }),
);

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const adaptiveLoadingPlugin = {
  requestWillFetch: async ({request}) => {
    const urlParts = request.url.split('/');
    let imageQuality;

    switch (
      navigator && navigator.connection
        ? navigator.connection.effectiveType
        : ''
    ) {
      //...
      case '3g':
        imageQuality = 'low_quality';
        break;
      //...
    }

    const newUrl = urlParts
      .splice(urlParts.length - 1, 0, imageQuality)
      .join('/')
      .replace('.jpg', '.png');
    
    const newRequest = new Request(newUrl.href, {headers: request.headers});

    return newRequest;
  },
};

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Advanced

App Shell

with Stream

PRECACHE

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PRECACHE

shell_header.html

shell_footer.html

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Dynamically changes

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Streaming

Fetch

Process

Fetch

Render

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registerRoute(/\.html$/,
  workbox.streams.strategy([

    // Get from cache 
    () => cacheFirst.handle({
        request: new Request("/shell_header.html"),
    }),

    //  Get the body from the network
    ({request}) => networkFirst.handle({
      request: `${request.url}?content=true`
    });

    // Get from cache 
    () => cacheFirst.handle({
        request: new Request("/shell_footer.html"),
    }),

  ]);
);

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Summary

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Agenda

  • Background Sync
  • Adaptive Loading
  • Advanced Caching
  • Stream

The web platform today is way more powerful than what we think!

 

let's embrace it!

Majid Hajian

mhadaily

Slides and link to source code

bit.ly/pwa-patterns

majid[at]softiware[dot]com

SVG icons credited to undraw.co

PWA, ADVANCED PATTERNS AND STRATEGIES

By Majid Hajian

PWA, ADVANCED PATTERNS AND STRATEGIES

Building progressive web apps has become the norm of web development these days! In fact, we are being introduced to more complex patterns and strategies to create a PWA. For example, When I built my book's website pwawithangular.com, I considered several caching strategies and patterns to deliver fully offline and high-performance web applications that can load under 2 seconds with 3G internet. In this talk, I will share how I could manage to build a fast and reliable PWA by using different caching strategies, advanced PWA architecture, and patterns.

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