The CacheStorage interface represents the storage for Cache objects.
The interface:
- Provides a master directory of all the named caches that can be accessed by a
ServiceWorker or other type of worker or window scope (you're not limited to only using it with service workers). - Maintains a mapping of string names to corresponding
Cache objects.
Use CacheStorage.open() to obtain a Cache instance.
Use CacheStorage.match() to check if a given Request is a key in any of the Cache objects that the CacheStorage object tracks.
You can access CacheStorage through the global caches property.
Note: CacheStorage always rejects with a SecurityError on untrusted origins (i.e. those that aren't using HTTPS, although this definition will likely become more complex in the future.) When testing on Firefox, you can get around this by checking the Enable Service Workers over HTTP (when toolbox is open) option in the Firefox Devtools options/gear menu. Furthermore, because CacheStorage requires file-system access, it may be unavailable in private mode in Firefox.
This code snippet is from the MDN simple service worker example (see simple service worker running live.) This service worker script waits for an InstallEvent to fire, then runs waitUntil to handle the install process for the app. This consists of calling CacheStorage.open to create a new cache, then using Cache.addAll to add a series of assets to it.
In the second code block, we wait for a FetchEvent to fire. We construct a custom response like so:
- Check whether a match for the request is found in the CacheStorage. If so, serve that.
- If not, fetch the request from the network, then also open the cache created in the first block and add a clone of the request to it using
Cache.put (cache.put(event.request, response.clone()).) - If this fails (e.g. because the network is down), return a fallback response.
Finally, return whatever the custom response ended up being equal to, using FetchEvent.respondWith.
self.addEventListener("install", (event) => {
event.waitUntil(
caches
.open("v1")
.then((cache) =>
cache.addAll([
"/",
"/index.html",
"/style.css",
"/app.js",
"/image-list.js",
"/star-wars-logo.jpg",
"/gallery/bountyHunters.jpg",
"/gallery/myLittleVader.jpg",
"/gallery/snowTroopers.jpg",
]),
),
);
});
self.addEventListener("fetch", (event) => {
event.respondWith(
caches.match(event.request).then((response) => {
if (response !== undefined) {
return response;
} else {
return fetch(event.request)
.then((response) => {
let responseClone = response.clone();
caches.open("v1").then((cache) => {
cache.put(event.request, responseClone);
});
return response;
})
.catch(() => caches.match("/gallery/myLittleVader.jpg"));
}
}),
);
});
This snippet shows how the API can be used outside of a service worker context, and uses the await operator for much more readable code.
async function getData() {
const cacheVersion = 1;
const cacheName = `myapp-${cacheVersion}`;
const url = "https://jsonplaceholder.typicode.com/todos/1";
let cachedData = await getCachedData(cacheName, url);
if (cachedData) {
console.log("Retrieved cached data");
return cachedData;
}
console.log("Fetching fresh data");
const cacheStorage = await caches.open(cacheName);
await cacheStorage.add(url);
cachedData = await getCachedData(cacheName, url);
await deleteOldCaches(cacheName);
return cachedData;
}
async function getCachedData(cacheName, url) {
const cacheStorage = await caches.open(cacheName);
const cachedResponse = await cacheStorage.match(url);
if (!cachedResponse || !cachedResponse.ok) {
return false;
}
return await cachedResponse.json();
}
async function deleteOldCaches(currentCache) {
const keys = await caches.keys();
for (const key of keys) {
const isOurCache = key.startsWith("myapp-");
if (currentCache === key || !isOurCache) {
continue;
}
caches.delete(key);
}
}
try {
const data = await getData();
console.log({ data });
} catch (error) {
console.error({ error });
}