Updating the cache when new resources become available with the JavaScript Cache API

23 Oct 2023

Caching is an important technique in web development that helps to improve the performance and user experience of a website or web application. One challenge that developers often face is ensuring that the cache is updated with new resources when they become available.

In JavaScript, the Cache API provides a solution to this problem. The Cache API allows you to store and retrieve responses from the cache, and it also provides methods to update the cache with new resources.

Checking for updates

To check if there are any updates available for a resource, you can use the match method of the Cache interface. This method takes a request object as a parameter and returns a promise that resolves to the response if an updated version of the resource is found in the cache.

Here’s an example of how you can use the match method to check for updates:

caches.open('my-cache')
  .then(cache => {
    return cache.match('/path/to/resource');
  })
  .then(response => {
    if (response) {
      // Resource found in cache, check for updates
      fetch('/path/to/resource')
        .then(newResponse => {
          if (newResponse.status === 200) {
            // New version of the resource is available, update the cache
            caches.open('my-cache')
              .then(cache => {
                cache.put('/path/to/resource', newResponse.clone());
              });
          }
        });
    }
  });

In the above example, we first open the cache using the caches.open method and then use the match method to check if the resource is already available in the cache. If the resource is found, we make a network request to fetch the latest version of the resource. If the response status is 200 (indicating a successful request), we update the cache using the put method.

Listening for updates

In addition to checking for updates manually, you can also listen for updates using the cache event. This event is fired whenever a resource is added, updated, or removed from the cache.

Here’s an example of how you can listen for updates using the cache event:

self.addEventListener('fetch', event => {
  event.respondWith(
    caches.match(event.request)
      .then(response => {
        if (response) {
          // Resource found in cache, check for updates
          fetch(event.request)
            .then(newResponse => {
              if (newResponse.status === 200) {
                // New version of the resource is available, update the cache
                caches.open('my-cache')
                  .then(cache => {
                    cache.put(event.request, newResponse.clone());
                  });
              }
            });
          return response;
        }
      })
  );
});

In this example, we add an event listener to the fetch event and use the respondWith method to intercept and handle network requests. The caches.match method is used to check if the requested resource is available in the cache. If it is found, we make a network request to fetch the latest version of the resource, update the cache if necessary, and return the cached response.

By using the match method and listening for cache updates, you can ensure that your cache is always up to date with the latest resources. This can greatly improve the performance and responsiveness of your web application.

Checking for updates

Listening for updates

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