sw.js

'use strict';

const cacheName = 'your-weather-app';
const filesToCache = [
    'index.html',
    'style.css'
];

self.addEventListener('install', e => {
    console.log('[ServiceWorker] Install');
    e.waitUntil(
        caches.open(cacheName).then(cache => {
            console.log('[ServiceWorker] Caching app shell');
            return cache.addAll(filesToCache);
        }).catch(err => console.log(err.stack))
    );
});

self.addEventListener('activate',  event => {
    event.waitUntil(self.clients.claim());
});

self.addEventListener('fetch', event => {
    event.respondWith(
        caches.match(event.request, {ignoreSearch:true}).then(response => {
            return response || fetch(event.request);
        }).catch(err => console.log(err.stack))
    );
});