service-worker.html

---js
{
    permalink: "service-worker.js",
    built: function () {
        let s = (new Date).toLocaleString('en-US', { hour12: false })
        s = s.slice(0, -3) // remove seconds
        s = s.replace(',', '').replace(':', '')
        s = s.replace(/(\d+)\/(\d+)\/(\d+) /, "$3$1$2-")
        return s
    }
}
---
'use strict';

const CACHE_NAME = "{{built}}";

const FILES = [
    {{> files }}
];

// NOTE: This is "install" of the service worker, not the app
self.addEventListener('install', (evt) => {
    evt.waitUntil(
        caches.open(CACHE_NAME)
            .then(cache =>
                Promise.all(
                    FILES.map(url => {
                        // cache-bust using a random query string
                        return fetch(`${url}?${Math.random()}`)
                            .then(response => {
                                if (!response.ok)
                                    throw Error('Not ok ' + url);
                                return cache.put(url, response);
                            });
                    })
                ))
            .then(() => self.skipWaiting()) // ???
    );
});

self.addEventListener('activate', (evt) => {
    evt.waitUntil(
        caches.keys()
            .then(keyList => Promise.all(keyList.map(key => {
                if (key !== CACHE_NAME)
                    return caches.delete(key);
                }))
            )
            .then(() => self.clients.claim()) // ???
    );
});

self.addEventListener('fetch', e => {
    e.respondWith(
        // return from cache if present else fetch
        // WARNING: don't use ignoreSearch - extremely slow on Chrome
        // https://stackoverflow.com/questions/41758252/service-worker-slow-response-times#41758253
        caches.match(e.request)
            .then(r => r || fetch(e.request))
    );
});