what is a service worker js code example

Example: service worker.js

if ('serviceWorker' in navigator) {  window.addEventListener('load', function() {    navigator.serviceWorker.register('/sw.js').then(function(registration) {      // Registration was successful      console.log('ServiceWorker registration successful with scope: ', registration.scope);    }, function(err) {      // registration failed :(      console.log('ServiceWorker registration failed: ', err);    });  });}