CacheOverride()

The CacheOverride constructor lets you configure the caching behavior of a Response.

Normally, the HTTP Headers on a Response would control how the Response is cached, but CacheOverride can be set on a Request, to define custom caching behavior.

Syntax

new CacheOverride(mode)
new CacheOverride(mode, init)

Note: CacheOverride() can only be constructed with new. Attempting to call it without new throws a TypeError.

Parameters

• mode : string

  • Sets the cache override mode for a request
  • If set to:
    • "none": Do not override the behavior specified in the origin response’s cache control headers.
    • "pass": Do not cache the response to this request, regardless of the origin response’s headers.
    • "override": Override particular cache control settings using the CacheOverride object's settings.

• init

  • : An Object which contains all the configuration options to apply to the newly created CacheOverride.

    • pci : boolean optional

      • Override the caching behavior of this request to enable or disable PCI/HIPAA-compliant non-volatile caching.
      • By default, this is false, which means the request may not be PCI/HIPAA-compliant. Set it to true to enable compliant caching.
      • See the Fastly PCI-Compliant Caching and Delivery documentation for details.

    • surrogateKey : string optional

      • Override the caching behavior of this request to include the given surrogate key, provided as a header value.
      • See the Fastly surrogate keys guide for details.

    • swr : number optional

      • Override the caching behavior of this request to use the given stale-while-revalidate time, in seconds

    • ttl : number optional

      • Override the caching behavior of this request to use the given Time to Live (TTL), in seconds.

Return value

A new CacheOverride object.

Examples

In this example we override the cache for all the requests prefixed /static/ to have a long TTL (Time To Live), and the home page to have a short TTL and a long SWR (Stale While Revalidate).

/// <reference types="@fastly/js-compute" />
import { CacheOverride } from "fastly:cache-override";
// In this example we override the cache for all the requests prefixed /static/ 
// to have a long TTL (Time To Live), and the home page to have a short TTL and 
// a long SWR (Stale While Revalidate).
async function app (event) {
  const path = (new URL(event.request.url)).pathname;
  let cacheOverride;
  if (path == '/') {
    cacheOverride = new CacheOverride('override', {ttl: 10, swr: 86_400});
  } else if (path.startsWith('/static/')) {
    cacheOverride = new CacheOverride('override', {ttl: 86_400});
  } else {
    cacheOverride = new CacheOverride('none')
  }
  return fetch(event.request.url, {
    cacheOverride,
    backend: 'origin_0'
  });
}
addEventListener("fetch", event => event.respondWith(app(event)));