v133 · network / connectivity
Round-trip Comparison
The JS Storage Access API requires multiple network round trips. The new header-based approach reduces this to a single round trip. Animate both flows side-by-side with configurable latency to see the real difference.
Configure latency
300 ms
JS API total
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Header API total
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Savings
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Round trips saved
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JS Storage Access API 3–4 round trips
1
Browser → Server
Initial subresource request (no cookies — partitioned context)
Initial subresource request (no cookies — partitioned context)
2
Server → Browser
Response signals login required; JS calls
Response signals login required; JS calls
document.requestStorageAccess()3
Browser → Server
Second request after access granted — now includes unpartitioned cookies
Second request after access granted — now includes unpartitioned cookies
4
Server → Browser
Final authenticated response returned
Final authenticated response returned
Storage Access Headers 1 round trip
1
Browser → Server
Request includes
Request includes
Sec-Fetch-Storage-Access: none (or active if permission cached)2
Server → Browser
Response includes
Response includes
Activate-Storage-Access: retry; allowed-origin="…"3
Browser → Server
Single retry with
Single retry with
Sec-Fetch-Storage-Access: active — cookies included4
Not needed — authenticated response already returned in step 3
Why it matters — requires no iframe
The JS Storage Access API requires the embedded resource to be in an
<iframe>. The header approach works for any subresource request (images, fetch, XHR), expanding authenticated embed support to CDN assets, API calls, and media without requiring an iframe.