First Steps with the Cache API

Flavio Copes

The Cache API was created to allow Service Workers to have a deeper and fine-grained control over the caching of resources.

Through the Cache API a Service Worker can decide to cache resources for offline consumption and retrieve them later.

With resources, we mean complete responses from URL, like HTML pages, CSS, JavaScript files, images, JSON, and any other resource that can be consumed by your web pages or web apps.

Browser Support

You can’t talk about recent web technology without detailing which are the browsers supported.

In the case of the Cache API, we are talking about:

  • Firefox 39 and higher
  • Chrome 40 and higher
  • Opera 29 and higher
  • Safari 11.1 and higher
  • iOS Safari 11.4 and higher
  • Edge 17 and higher
  • UC Browser 11.8 and higher
  • Chrome for Android 67 and higher

There is no support for Internet Explorer.

Other than Firefox and Chrome, support in other browsers has been introduced really recently, so you should keep this in mind.

Your sites and applications, if you plan to support more than just people that run the browsers above mentioned, should have any Cache API code inside this check:

if ('caches' in window) {
  // The Cache API is supported

  // You can add your code here
}

Working with caches

if ('caches' in window) {
  // The Cache API is supported
  const cacheName = 'my-website-cache'
  caches.open(cacheName).then(cache => {
    // you can start using the cache
  })
}

A cache is linked to the current origin (domain), and for security and privacy reasons you cannot access caches set up for others.

You can set up several different caches. To see all the caches set up for the current origin, you can iterate over caches.keys():

caches.keys().then(keys => {
  keys.map(key => {
    console.log(key)
  })
})

You can delete one cache by calling the delete() method:

const cacheName = 'my-website-cache'
caches.delete(cacheName).then(() => {
  console.log('Cache deleted')
})

Adding to a cache

We have 3 methods:

  • cache.put()
  • cache.add()
  • cache.addAll()

You call cache.put() in the successful promise callback of a fetch() call:

const cacheName = 'my-website-cache'
const url = '/resource'
fetch(url).then(res => {
  return caches.open(cacheName).then(cache => {
    return cache.put(url, res)
  })
})

With cache.add() you don’t manually have to fetch the resource prior to adding it to the cache: the Cache API makes this automatically for you.

const cacheName = 'my-website-cache'
const url = '/resource'
caches.open(cacheName).then(cache => {
  cache.add(url).then(() => {
    //done!
  }
})

In this case, following the cache.add() call, a Fetch request is sent to the server, and the response is cached.

cache.addAll() is used to perform requests to multiple URLs. The callback function is only called when all the resources have been fetched and cached:

const cacheName = 'my-website-cache'
const url1 = '/resource1'
const url2 = '/resource2'
caches.open(cacheName).then(cache => {
  cache.addAll([url1, url2]).then(() => {
    //all requests were cached
  })
})

Retrieving from a cache

Using cache.match() you can get the Response object that was stored corresponding to the URL that matches your query:

const cacheName = 'my-website-cache'
const url = '/resource'
caches.open(cacheName).then(cache => {
  cache.match(url).then(item => {
    console.log(item)
  }
})

item is a Request object which you can inspect, for example, you can get the URL using item.url.

Iterate Over All Items in the Cache

Using cache.keys() you can get all the items that are present in a cache, and iterate over them:

const cacheName = 'my-website-cache'
const url = '/resource'
caches.open(cacheName).then(cache => {
  cache.keys().then(items => {
    items.map(item => {
      console.log(item)
    })
  }
})

Each item is a Request object.

Removing an item from the cache

Once a resource is added to the cache, it takes up some amount of space in the browser’s storage. You can manually clear anything you stored by its original URL, passing it to the cache.delete() method:

const cacheName = 'my-website-cache'
const url = '/resource'
caches.open(cacheName).then(cache => {
  cache.delete(url).then(() => {
    //deleted successfully!
  }
})
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