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Cache API in JavaScript

Learn how to cache resources with Cache API in JavaScript.

Cache API Cheat-sheet
The Cache API allows Service Workers to have a control over resources(HTML pages, CSS, JavaScript files, images, JSON, etc) to be cached. Through Cache API a Service Worker can cache resources for offline and retrieve them later.
Detecting the cache support
Check if the caches object available in window.
let isCacheSupported = 'caches' in window;
caches is an instance of CacheStorage .
Creating/Initialize Cache
We can create a cache with name using open method, which will returns a promise . If the cache already exists , then it don’t create a new cache.
caches.open('cacheName').then( cache => {
});
You cannot you cannot access caches set up for others origin(domain).
The cache which you’r are creating will be created for your domain.
You can add multiple cache for same domain, which you can access by caches.keys()
Adding an item to cache
You can cache a resource using three methods add , addAll , set . add() and addAll() method automatically fetches a resource, and caches it, whereas in set method we will fetch a data and set the cache.
1.add
let cacheName = 'userSettings'; 
let url = '/api/get/usersettings';
caches.open(cacheName).then( cache => {
   cache.add(url).then( () => {
       console.log("Data cached ")
    });
});
In thee above code, internally a request for /api/get/usersettings url is sent to server, once the data is received, the response will be cached.
2.addAll
addAll accepts an array of URL , and returns a promise when all the resources are cached.
let urls = ['/get/userSettings?userId=1', '/get/userDetails'];
caches.open(cacheName).then( cache => {
cache.addAll(urls).then( () => {
       console.log("Data cached ")
    });
});
Cache.add/Cache.addAll do not cache responses with Response.status values that are not in the 200 range, Cache.put lets you store any request/response pair.
3. put
put adds a key/value pairs to current Cache object.In put we need to manually fetch the request and set the value.
Note: put() will overwrite any key/value pair previously stored in the cache that matches the request.
let cacheName = 'userSettings';
let url = '/api/get/userSettings';
fetch(url).then(res => {
  return caches.open(cacheName).then(cache => {
    return cache.put(url, res);
  })
})
Retrieving from a cache
Using cache.match() you can get the Response that was stored to the URL .
const cacheName = 'userSettings'
const url = '/api/get/userSettings'
caches.open(cacheName).then(cache => {
  cache.match(url).then(settings => {
    console.log(settings);
  }
});
The settings is a Response Object, which looks like
Response {
  body: (...),
  bodyUsed: false,
  headers: Headers,
  ok: true,
  status: 200,
  statusText: "OK",
  type: "basic",
  url: "https://test.com/api/get/userSettings"
}
Retrieve All Items in the Cache
The cache object contains keys methods which will have all the url of the current cache object.
caches.open(cacheName).then( (cache) => { 
  cache.keys().then( (arrayOfRequest) => { 
      console.log(arrayOfRequest); // [Request,  Request]
  });
});
arrayOfRequest is an array of Request objects, which has all details about the request.
Retrieving all caches
caches.keys().then(keys => {
  // keys is an array with the list of keys
})
Remove an item from the cache
You can use delete method on cache object to remove a particular cached Request.
let cacheName = userSettings; 
let urlToDelete = '/api/get/userSettings';
caches.open(cacheName).then(cache => {
  cache.delete(urlToDelete)
})
Remove the cache completely
caches.delete(cacheName).then(() => {
   console.log('Cache successfully deleted!');
})

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