Add Service Worker
https://github.com/GoogleChrome/sw-precache#install
$ npm install --save-dev sw-precache
sw-precache --config=path/to/sw-precache-config.js --verbosehttps://codelabs.developers.google.com/codelabs/sw-precache/#5
Add the following <script> tag to the bottom of your index.html file to register your service worker:
<script>
if ('serviceWorker' in navigator) {
navigator.serviceWorker.register('/sw.js').then(function() {
console.log("Service Worker Registered");
});
}
</script>How does SW-Precache works
ref: https://medium.com/@Huxpro/how-does-sw-precache-works-2d99c3d3c725