On Wed, Feb 26, 2020 at 9:29 PM Maciej Stachowiak <mjs@apple.com> wrote:
I also suggest to start with "first-paint" as it's perhaps a bit less "internal" than FCP, and can provide a performance-regression metric with a lesser degree of risk regarding exposing internals / privacy.
First paint that’s not first meaningful/contentful paint is not a very good performance metric IMO. Who cares that a paint happened if it doesn’t have any image or text content?
I think it's meaningful as a general regression metric, albeit less useful than FCP. Web developers are scrambling for any RUM information they can use...
I also don’t think this exposes less. The privacy risk here is exposing timing data that might be usable for fingerprinting.
Yes, I think that privacy-relevant timing information is already available through resource timing (window.performance.getEntries("resource")). But we'll see what the privacy experts come up with.
What was deprecated was "first meaningful paint" (FMP). FCP was not deprecated and has been in wide use for some time.
What’s the difference between First Meaningful and First Contentful?
FMP had the notion of "primary" content; e.g. it was ignoring navbars/headers, and trying to figure out when the main content of the site has been rendered. As noted, FMP is deprecated. FCP is a lot more transparent in what it measures. We will discuss with Apple’s privacy experts what they think of the privacy
risk. I’m just giving you a rain check for results of this discussion.
Got it, Looking forward :)