Cache HTTP responses with the Web Cache API
Deno implements the Web Cache API from service workers. The caches global stores Response objects keyed by request URL, persisted on disk between runs, and the same code works on Deno Deploy. This example starts a local server that counts requests, then proves a cached fetch helper only hits the server once.
This server counts how many requests actually reach it. Port 0 asks the operating system for any free port.
let requestCount = 0;
const server = Deno.serve({ port: 0, onListen: () => {} }, () => {
requestCount++;
return new Response(JSON.stringify({ message: "hello" }), {
headers: { "content-type": "application/json" },
});
});caches.open returns a named cache, creating it on first use. No extra permission flags are needed for the cache itself.
const cache = await caches.open("example-cache-v1");The helper tries the cache first and falls back to the network. A response body can be read only once, so store a clone and return the original.
async function cachedFetch(url: string): Promise<Response> {
const cached = await cache.match(url);
if (cached) {
return cached;
}
const response = await fetch(url);
await cache.put(url, response.clone());
return response;
}The first call misses the cache and reaches the server.
const url = `http://localhost:${server.addr.port}/data`;
const first = await cachedFetch(url);
console.log(await first.json()); // { message: "hello" }The second call is served from the cache.
const second = await cachedFetch(url);
console.log(await second.json()); // { message: "hello" }The server saw exactly one request, so the cache really answered the second call.
console.log(requestCount); // 1cache.delete removes a single entry, caches.delete removes the whole named cache. Both return whether something was deleted.
console.log(await cache.delete(url)); // true
console.log(await caches.delete("example-cache-v1")); // true
await server.shutdown();Run this example locally using the Deno CLI:
deno run -N https://docs.deno.com/examples/scripts/web_cache_api.ts