Understanding the Difference Between 'reload' and 'no-cache' Cache Modes in the Fetch API

When working with the Fetch API, you might have come across different cache modes that control how requests interact with the browser’s cache. Two of these cache modes, reload and no-cache, involve making network requests to fetch resources or validate their freshness. Although they might seem similar at first glance, they have distinct behaviors that affect how efficiently your application uses the cache. In this blog post, we’ll explore the differences between reload and no-cache cache modes and their impact on web performance.

Cache Modes in the Fetch API

Before diving into reload and no-cache” cache modes, let’s have a quick look at the available cache modes in the Fetch API:

  1. default: The browser performs the default cache behavior.
  2. no-store: The browser bypasses the cache and doesn’t store the fetched response.
  3. reload: The browser fetches the resource from the network, ignoring the cache, and stores the fetched response in the cache.
  4. no-cache: The browser checks the cache for the resource, validates its freshness with the server, and updates the cache if necessary.
  5. force-cache: The browser uses the cached response if available and fetches the resource from the network if the cache is unavailable or stale.
  6. only-if-cached: The browser uses the cached response if available and returns an error if the resource is not in the cache.

Now let’s take a closer look at the differences between reload and no-cache cache modes.

“reload” Cache Mode

The reload cache mode forces the browser to fetch the resource directly from the network, bypassing the cache. Once the resource is fetched, the browser stores the new response in the cache, replacing any existing cached data for that resource. In this mode, a full network request is made every time, regardless of the freshness of the cached data.

Example reload request:

GET /resource HTTP/1.1
Host: example.com
Cache-Control: no-cache

Example reload response (resource fetched from the network):

HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
ETag: "new-etag-value"
Last-Modified: Mon, 15 Jan 2023 00:00:00 GMT

<!-- Resource content here -->

“no-cache” Cache Mode

The no-cache cache mode tells the browser to check the cache for the resource first. If the resource is found in the cache, the browser sends a conditional request to the server to verify the freshness of the cached data. The server checks the resource’s freshness using cache-related headers (e.g., ETag, Last-Modified) provided in the request. If the server determines that the cached data is still fresh, it responds with a 304 Not Modified status, indicating that the cached data can be used. In this case, the browser doesn’t download the resource again, saving bandwidth and reducing load time. However, if the server indicates that the cached data is stale or has been modified, the browser fetches the updated resource from the network and updates the cache.

Example no-cache request (with a cached response that has ETag and Last-Modified headers):

GET /resource HTTP/1.1
Host: example.com
Cache-Control: no-cache
If-None-Match: "some-etag-value"
If-Modified-Since: Mon, 01 Jan 2023 00:00:00 GMT

Example no-cache response (resource fetched from the network):

HTTP/1.1 200 OK
Content-Type: text/html; charset=utf-8
ETag: "new-etag-value"
Last-Modified: Mon, 15 Jan 2023 00:00:00 GMT

<!-- Resource content here -->

Example no-cache response (cached response is still fresh):

HTTP/1.1 304 Not Modified
ETag: "some-etag-value"
Last-Modified: Mon, 01 Jan 2023 00:00:00 GMT

Summary

The key difference between reload and no-cache cache modes is in the way they use the cache:

  • reload always bypasses the cache and fetches the resource from the network, even if the cached data is fresh. This can result in unnecessary network requests and increased load times.
  • no-cache validates the freshness of the cached data with the server before fetching it from the network. If the cached data is still fresh, the browser doesn’t download the resource again, saving bandwidth and reducing load time.

Understanding the differences between these cache modes and how they affect web performance can help you make informed decisions when designing and optimizing your applications. By using the appropriate cache mode for your specific use case, you can ensure that your application delivers an efficient and responsive user experience.

Mar 16, 2023