removeOldCache.js

async function removeOldCache(event) {
	await caches.keys().then(function (keys) {
		return Promise.all(keys.filter(function (key) {
			return key !== VERSION;
		}).map(function (key) {
			return caches.delete(key);
		}));
	}).then(function () {
		return self.clients.claim();
	});
}