[PWA] 7. First Cache when installed

If you want your application works offline or lie-wifi. You need to use cache.

API:

Create Caches:

caches.open('cache_name').then( (cache) => {
    // create name if not exists yet, return cache if there is a one
})

Create single cache:

cache.put(request, response);

cache.addAll([
  '/foo',
  '/bar'
])

Get the cache:

cache.match(request)

caches.match(request)

When to start cache:

We can do cache in 'installing' service worker, what it will do is fetch everything we need from network and create cache for each of them.

self.addEventListener('install', function(event) {
  var urlsToCache = [
    '/',
    'js/main.js',
    'css/main.css',
    'imgs/icon.png',
    'https://fonts.gstatic.com/s/roboto/v15/2UX7WLTfW3W8TclTUvlFyQ.woff',
    'https://fonts.gstatic.com/s/roboto/v15/d-6IYplOFocCacKzxwXSOD8E0i7KZn-EPnyo3HZu7kw.woff'
  ];

  event.waitUntil(
    // TODO: open a cache named 'wittr-static-v1'
    // Add cache the urls from urlsToCache
      caches.open('wittr-static-v1')
          .then( (cache) => {
              cache.addAll(urlsToCache)
          })
          .catch( () => {
              console.error("Cannot cache anything");
          })
  );
});

Now we have create the cache, but it is not useful until we use the cache.

To use cache, we can do:

self.addEventListener('install', function(event) {
  var urlsToCache = [
    '/',
    'js/main.js',
    'css/main.css',
    'imgs/icon.png',
    'https://fonts.gstatic.com/s/roboto/v15/2UX7WLTfW3W8TclTUvlFyQ.woff',
    'https://fonts.gstatic.com/s/roboto/v15/d-6IYplOFocCacKzxwXSOD8E0i7KZn-EPnyo3HZu7kw.woff'
  ];

  event.waitUntil(
    // TODO: open a cache named 'wittr-static-v1'
    // Add cache the urls from urlsToCache
      caches.open('wittr-static-v4')
          .then( (cache) => {
              cache.addAll(urlsToCache)
          })
          .catch( () => {
              console.error("Cannot cache anything");
          })
  );
});

self.addEventListener('fetch', function(event) {
    event.respondWith(
        caches.match(event.request).then((response)=>{
            if(response){
                return response;
            }else{
                return fetch(event.request);
            }
        })
    )
});

So we use 'caches.match' to get all the caches for request.

In the then block, cache is successfully fetched, we check whether there is cache data, if it is, then return the response;

If there is no cache data, then we fetch the data from real-server.

But this approach has some problem:

After we go offline mode, the pictures are not showing, this is because we only cache when the servcie worker is installed. 

So here is some problem we need to solve: