install.js

self.addEventListener('install', (event) => {
    let CACHE_NAME = 'xyz-cache'
    let urlsToCache = [
        '/',
        '/styles/main.css',
        '/scripts/bundle.js'
    ]
    event.waitUntil(
        /* open method available on caches, takes in the name of cache as the first paramter. It returns a promise that resolves to the instance of cache
        All the above URLS can be added to cache using the addAll method. */
        caches.open(CACHE_NAME)
        .then (cache => cache.addAll(urlsToCache))
    )
})