PerformanceResourceTiming: deliveryType property

A string, which can be one of the following values:

"cache"

The resource was retrieved from the cache.

"navigational-prefetch" Experimental

The resource was retrieved from a prefetched response stored in an in-memory cache via the Speculation Rules API.

"" (empty string)

Returned if none of the above delivery types apply.

The deliveryType property can be used to get specific resource timing entries only; for example, only those that were cached.

The following example uses a PerformanceObserver to notify of new resource performance entries as they are recorded in the browser's performance timeline. The buffered option is used for accessing entries from before the observer creation.

const observer = new PerformanceObserver((list) => {
  const cachedResources = list.getEntries().filter((entry) => {
    return entry.deliveryType === "cache";
  });
  console.log(cachedResources);
});

observer.observe({ type: "resource", buffered: true });

The following example uses Performance.getEntriesByType(), which only shows resource performance entries present in the browser's performance timeline at the time you call the method.

const scripts = performance.getEntriesByType("resource").filter((entry) => {
  return entry.deliveryType === "cache";
});
console.log(scripts);