How to use the http-cache-semantics function in http-cache-semantics

async function handleInitialFetch(args: {request: Request, key: string}) {
	let {request, key} = args

	debug && console.log(`fetch(${request.url}): no policy cached; fetching`)

	// I explicitly want errors here to propagate. Why? Bundled data will have
	// an expired policy stored, so it won't hit this branch. Thus, the only
	// requests in here will have nothing to fall back to, so we need some way
	// to signal that an error happened.
	let response = await fetch(request)

	let cachePolicyRequest = requestForCachePolicy(request)
	let cachePolicyResponse = responseForCachePolicy(response)

	let policy = new CachePolicy(cachePolicyRequest, cachePolicyResponse)

	if (policy.storable()) {
		debug && console.log(`fetch(${request.url}): caching`)
		await cacheItem({key, response, policy})
	} else {
		debug && console.log(`fetch(${request.url}): not cachable`)
	}

	return response
}

export async function insertForUrl(url: string, data: mixed) {
	let key = `urlcache:${url}`

	let {policy: oldPolicy} = await getItem(key)

	if (oldPolicy) {
		return
	}

	let req = new Request(url)
	let resp = new Response(JSON.stringify(data), {status: 200})
	let policy = new CachePolicy(
		requestForCachePolicy(req),
		responseForCachePolicy(resp),
	)

	return cacheItem({key, response: resp, policy, bundled: true})
}