Browser & Web Performance · Middle · Question 71 of 75

Why does Resource Timing show zeros for DNS, connect and request phases of some cross-origin resources?

1Those resources came from a service worker
2The browser doesn't measure cross-origin requests at all
✓Correct answer: Detailed timings of cross-origin resources are hidden unless the server sends Timing-Allow-Origin

Explanation

Timing details could leak information across origins, so they're opt-in. Your own CDN should send the header.

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