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Angular 5 Service Workers – Caching, Life Cycle, Register, Install, Design Goal and Advantages!

What Is Service Workers?
A Service Worker is a script which runs in the web browsers and manages to the caching for web applications. This script runs in the separates and background and don't need any user interactions.

They can query a local cache and deliver a cached response, if it is available in the cached. This makes more reliable and increase the performance.

A Service Worker is a programmable network proxy and it intercept all outgoing HTTP requests and use to allowing you to control how network requests from your page are handled.

The Service Worker is a method that enables applications to take advantage of persistent data in the background processing, including hooks to enable bootstrapping of web applications while offline.

What Is Service Workers in Angular 5+?
Angular 5+ start using service workers and the service workers are increased the apps reliability and performance without needing to code against this.

This is the great advantages for angular and Angular’s service worker is designed for -
ü  Improve the performance regarding the unreliable network connection
ü  Minimizing the risks of serving outdated content
ü  It’s Optimize the end user experience

The main Design Goal of Angular's Service Worker -
ü  Caching an application
ü  When users refresh applications, they see firstly latest version cached file.
ü  The Updates happen in the background process. Do not interrupt to other process.
ü  When Updates, it’s happen the previous version of the application is served until an update ready to use

Prerequisites to Supports Service Workers
We must have the following Angular and Angular CLI versions and also our web application must run in a web browser that supports service workers.
ü  Angular 5 or later
ü  Angular CLI 1.6 or later

What Is Service Worker Life Cycle?
A service worker has a life cycle that is completely separate from your web apps page.
To install a service worker for our site, we need to register it, which we do in our pages. To Registering a service worker will cause the browser to start the service worker install step in the background process.

Prerequisites to Supports Service workers-
ü  Browser support
ü  You need HTTPS

How To Register A Service Worker?
To install a service worker you need to kick start the process by registering it in your page. This tells the browser where your service worker JavaScript file lives.

You can call below register () every time a page loads without concern; the browser will figure out if the service worker is already registered or not and handle it accordingly.

if ('serviceWorker' in navigator) {
  window.addEventListener('load', function() {
    navigator.serviceWorker.register('/sw.js').then(function(registration) {
      // If Registration was successful
      console.log('Success Registration - ', registration.scope);
    },
    function(err) {
      // If Registration was failed!
      console.log('Failed Registration - ', err);
    });
  });
}

This code checks to see if the service worker API is available, and if it is, the service worker at /sw.js is registered once the page is loaded.

How To Install a Service Worker?
After a controlled page kicks off the registration process, let's shift to the point of view of the service worker script, which handles the install event.

Example looks like -
self.addEventListener('install', function(event) {
  // Perform install steps
});

Inside of our install callback, we need to take the following steps -
ü  Open a cache
ü  Cache our files
ü  Confirm whether all the required assets are cached or not

Example looks like -
var CACHE_NAME = 'my-site-cache-v1.0';
var urlsToCache = [
  '/',
  '/styles/site.css',
  '/script/site.js'
];

self.addEventListener('install', function(event) {
  // Perform install steps
  event.waitUntil(
    caches.open(CACHE_NAME)
      .then(function(cache) {
        console.log('Opened cache');
        return cache.addAll(urlsToCache);
      })
  );
});

How To Cache and return Requests?
After a service worker is installed and the user navigates to a different page or refreshes, the service worker will begin to receive fetch events.

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

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By Anil Singh | Rating of this article (*****)

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