Introduction

Progressive Web App (PWA) are web applications that are regular web pages or websites but can appear to the user like traditional applications or native mobile applications. The application type attempts to combine features offered by most modern browsers with the benefits of mobile experience. Open Event web app is a web application generator which has now introduced this new feature in its generated applications.

Why Progressive Web Apps?

The reasons why we enabled this functionality are that PWAs are –

• Reliable – Load instantly and never show the downasaur, even in uncertain network conditions.
• Fast – Respond quickly to user interactions with silky smooth animations and no janky scrolling.
• Engaging – Feel like a natural app on the device, with an immersive user experience.

Thus where Open Event Web app generated applications are informative and only requires one time loading with functionalities like bookmarks depending on local storage of browser, we found Progressive web apps perfect to explain and demonstrate these applications as a whole.

How PWAs work?

The components associated with a progressive web application are :

Manifest: The web app manifest is a W3C specification defining a JSON-based manifest to provide developers a centralized place to put metadata associated with a web application.

Service Workers: Service Workers provide a scriptable network proxy in the web browser to manage the web/HTTP requests programmatically. The Service Workers lie between the network and device to supply the content. They are capable of using the cache mechanisms efficiently and allow error-free behavior during offline periods.

How we turned Open event Web app to a PWA?

Adding manifest.json

 {
"icons": [
    {
      "src": "./images/logo.png",
      "type": "image/png",
      "sizes": "96x96"
    }
  ],
  "start_url": "index.html",
  "scope": ".",
  "display": "standalone",
  "orientation": "portrait-primary",
  "background_color": "#fff",
  "theme_color": "#3f51b5",
  "description": "Open Event Web Application Generator",
  "dir": "ltr",
  "lang": "en-US"
}

Adding service workers

The initialization of service workers is done by calling an event listener namely ‘install’ :

var urlsToCache = [
 './css/bootstrap.min.css',
 './offline.html',
 './images/avatar.png'
];

self.addEventListener('install', function(event) {
 event.waitUntil(
   caches.open(CACHE_NAME).then(function(cache) {
     return cache.addAll(urlsToCache);
   })
 );
});

The service workers fetch the data from the cache when event listener ‘fetch’ is triggered. When a cache hit occurs the response data  is sent to the client from there otherwise it tries to fetch the data by making a request to the network. In case when network does not send response status code ‘200’, it sends an error response otherwise caches the data received.

self.addEventListener('fetch', function(event) {
 event.respondWith(
   caches.match(event.request).then(function(response) {
     // Cache hit - return response
     if (response) {
       return response;
     }

     var fetchRequest = event.request.clone();

     return fetch(fetchRequest)
       .then(function(response) {
         if (
           !response ||
           response.status !== 200 ||
           response.type !== 'basic'
         ) {
           return response;
         }
         var responseToCache = response.clone();
         caches.open(CACHE_NAME).then(function(cache) {
           cache.put(event.request, responseToCache);
         });
         return response;
       })
       .catch(function(err) {
         if (event.request.headers.get('Accept').indexOf('text/html') !== -1) {
           return caches.match('./offline.html');
         } else if (event.request.headers.get('Accept').indexOf('image') !== -1) {
           return caches.match('./images/avatar.png');
         } else {
           console.log(err);
         }
       });
   })
 );
});

The service workers are activated through the event listener namely ‘activate’ :

self.addEventListener('activate', function(event) {
 event.waitUntil(
   caches.keys().then(function(cacheNames) {
     return Promise.all(
       cacheNames.map(function(cacheName) {
         if (cacheName !== CACHE_NAME) {
           console.log('Deleting cache ' + cacheName);
           return caches.delete(cacheName);
         }
       })
     );
   })
 );
});

Adding service workers and manifest to the generator

Since we need to add the service workers and manifest to every web application generated through app generator, we copy the files ‘sw.js’ and ‘manifest.json’ in the directory structure of that particular web app using filestream module with the help of two abstract functions ‘copyServiceWorker’ and ‘copyManifestFile’ present in ‘distHelper.js’ code file.

distHelper.copyServiceWorker(appFolder, hashObj['hash'], function (err) {
 if (err) {
   console.log(err);
   logger.addLog('Error', 'Error occurred while copying service worker file', socket, err);
   return done(err);
 }
 return done(null);
});

distHelper.copyManifestFile(appFolder, eventName, function(err) {
 if (err) {
   console.log(err);
   logger.addLog('Error', 'Error occured while copying manifest file', socket, err);
   return done(err);
 }
 return done(null);
});

Further Improvements

Enabling push notifications for the bookmarked tracks and sessions. The user would be notified about the upcoming events through the notifications in the way the native mobile applications do.

Resources

• Open Event Web app Repository: https://github.com/fossasia/open-event-webapp
• Pull Request: https://github.com/fossasia/open-event-webapp/pull/1549
• Issue: https://github.com/fossasia/open-event-webapp/issues/1219
• Intro to PWAs: https://codelabs.developers.google.com/codelabs/your-first-pwapp/