Websites can indicate that a particular Client Hint is critical to the page by including it in a `Critical-CH` HTTP response header. Doing so will trigger a connection restart if the hint listed in the `Critical-CH` HTTP response header could be (but wasn’t) included in the HTTP request initially sent. This intent proposes adding `readonly attribute DOMHighResTimeStamp criticalCHRestart;` to the `PerformanceNavigationTiming` interface.
It’s possible for websites to observe a change in the Navigation Timing related to `responseStart` and `requestStart`, but there is no explicit timestamp that indicates when this occurred. Without that it’s harder for sites to detect the impact that the `Critical-CH` HTTP response header has on connections. Developers (including Akamai) are interested in using this to better understand the impact of User Agent Client Hints / User Agent Reduction.
`criticalCHRestart` can only be set for top-level frames, as subresources and iframes ignore `Critical-CH` HTTP response headers.
N/A, this is a small, incremental addition to an existing feature for convenience and the loaded website has other (less convenient) ways to detect a Critical-CH restart.
We would be the first to implement if approved.
Web Developers: Requested by Akamai
Is this feature fully tested by web-platform-tests?
No, but it will be.
Link to entry on the Chrome Platform Status
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