3 ms·

const start = window.performance.now(); const t = await fetch("https://example.com/asset_that_may_be_cached.jpg"); const end = window.performance.now(); i

const start = window.performance.now(); const t = await fetch("https://example.com/asset_that_may_be_cached.jpg"); const end = window.performance.now(); if (end - start < 10/*ms*/) { console.log("cached"); } else { console.log("not cached"); }

amelius 6y ago
In that case, the browser would always load the asset (it is not cached). So the rule would be that only stuff that is directly in the <head> may be cached (or stuff that is on the same domain).
- tylerhou 6y ago
  To be clear, the context of the thread is "why do we need to partition the HTTP cache per domain." My example code works under the (soon-to-be-false) assumption that the cache is NOT partitioned (i.e. there is a global HTTP cache). > In that case, the browser would always load the asset (it is not cached). Agreed, if the cache is partitioned per domain AND the current domain has not requested the resource on a prior load. If the cache is global, then the asset will be loaded from cache if it is present: https://developer.mozilla.org/en-US/docs/Web/API/Request/cache https://developer.mozilla.org/en-US/docs/Web/API/Request/cac... > So the rule would be that only stuff that is directly in the <head> may be cached (or stuff that is on the same domain). You could be more precise here: with a domain-partitioned cache, all resources regardless of domain loaded by any previous request on the same domain could be cached. So if I load HN twice and HN uses https://example.com/image.jpg https://example.com/image.jpg on both pages, then the second request will use the cached asset.
  - amelius 6y ago
    > To be clear, the context of the thread is "why do we need to partition the HTTP cache per domain." Ah right, the thread is becoming long :) > So if I load HN twice and HN uses https://example.com/image.jpg https://example.com/image.jpg on both pages, then the second request will use the cached asset. Good point!

amelius 6y ago

In that case, the browser would always load the asset (it is not cached). So the rule would be that only stuff that is directly in the <head> may be cached (or stuff that is on the same domain).

tylerhou 6y ago
To be clear, the context of the thread is "why do we need to partition the HTTP cache per domain." My example code works under the (soon-to-be-false) assumption that the cache is NOT partitioned (i.e. there is a global HTTP cache). > In that case, the browser would always load the asset (it is not cached). Agreed, if the cache is partitioned per domain AND the current domain has not requested the resource on a prior load. If the cache is global, then the asset will be loaded from cache if it is present: https://developer.mozilla.org/en-US/docs/Web/API/Request/cache https://developer.mozilla.org/en-US/docs/Web/API/Request/cac... > So the rule would be that only stuff that is directly in the <head> may be cached (or stuff that is on the same domain). You could be more precise here: with a domain-partitioned cache, all resources regardless of domain loaded by any previous request on the same domain could be cached. So if I load HN twice and HN uses https://example.com/image.jpg https://example.com/image.jpg on both pages, then the second request will use the cached asset.
- amelius 6y ago
  > To be clear, the context of the thread is "why do we need to partition the HTTP cache per domain." Ah right, the thread is becoming long :) > So if I load HN twice and HN uses https://example.com/image.jpg https://example.com/image.jpg on both pages, then the second request will use the cached asset. Good point!