Progressive Web Apps (PWA) are web applications that have been designed so they are capable (utilize native features), reliable (work even in offline mode), and installable. These three pillars transform them into an experience that feels like a platform-specific application.
Why use PWA?
At their heart, Progressive Web Apps are just web applications. Using progressive enhancement, new capabilities are enabled in modern browsers. Using service workers and a web app manifest, a web application can be converted into a PWA. If the new capabilities aren't available, users still get the core experience.
As it can be seen from the picture above, PWA offers the best of both worlds by delivering a web experience your users will love, using the latest web features to bring enhanced capabilities and reliability, Progressive Web Apps allow what you build to be installed by anyone, anywhere, on any device with a single codebase.
Getting Started
The requirements for a website to be turned into a PWA are:
The website itself (served over https or from localhost)
manifest.json (provides information about a web application)
service worker (a script that allows intercepting and control of how a web browser handles its network requests and asset caching.)
Here we will not be focusing on creating a website, but on making an existing website installable. To follow along just use a basic website like the one given below.
NOTE: Its possible to style the site or add scripts, but for the purpose of adding PWA installation feature, this will suffice.
The defination of manifest.json
{"name":"<name of the application>","short_name":"<short name for the application> (can be same as name)","start_url":"<start url for the website>","display":"<display mode for the website>","description":"<description of the application>","background_color":"<color>","theme_color":"<color>","orientation":"<orientation>","icons":[{"src":"<image source>","sizes":"<widthxheight>","type":"image/png"}]}
An example manifest.json would look like
{"name":"PWA: Installable website","short_name":"Installable PWA","start_url":"index.html","display":"standalone","description":"App for testing PWA features","background_color":"#ffffff","theme_color":"#000000","orientation":"portrait-primary","icons":[{"src":"image/icon-24.png","sizes":"24x24","type":"image/png"},{"src":"image/icon-32.png","sizes":"32x32","type":"image/png"},{"src":"image/icon-48.png","sizes":"48x48","type":"image/png"},{"src":"image/icon-64.png","sizes":"64x64","type":"image/png"},{"src":"image/icon-128.png","sizes":"128x128","type":"image/png"},{"src":"image/icon-256.png","sizes":"256x256","type":"image/png"}]}
To add the manifest to the website, add the following in the head section
<linkrel="manifest"href="manifest.json"/>
Its a good practice to add the following in the head section as well for iOS support
Now only the service worker is left to be dealt with.
service-worker.js
constSTATIC_CACHE="static-cache-v1"conststatic_assets=["/","/index.html","/script.js","/image/icon-24.png","/image/icon-32.png","/image/icon-48.png","/image/icon-64.png","/image/icon-72.png","/image/icon-96.png","/image/icon-128.png","/image/icon-256.png",]// storing static assets in cache on service worker installself.addEventListener("install",event=>{event.waitUntil(caches.open(STATIC_CACHE).then(cache=>{cache.addAll(static_assets)}))})// returning static assets from cacheself.addEventListener("fetch",event=>{event.respondWith(caches.match(event.request).then(response=>{returnresponse||fetch(event.request);}))});
We are required to handle the fetch event to enable installation.
Enable the service worker by adding the following script in the website
<script>if('serviceWorker'innavigator){navigator.serviceWorker.register('/service-worker.js');}else{console.log("Service worker is not supported");}</script>
Now the last piece of the puzzle, serving the website on localhost. If you are using VS Code, you can easily do it using the live server extension (recommended for beginners).
The installation icon on the top right of the url-bar signifies its now installable. Click it to install the pwa on your device.
NOTE: This is just a brief overview. In a production grade pwa its more advisible to periodically refresh the static assets as well to ensure that the user don't access outdated content.
Tapajyoti Bose
