Report perf metrics on soft navigations
We (and others) have long been interested in making softnavigations more of a first-class experience in Lighthouse. You should be able to know the LCP, FCP, Speed index, etc for that softnav, just like you do for a hard nav.
soft navs are (almost) a thing: https://github.com/WICG/soft-navigations there's several heuristics to be satisfied (either with the new Navigation API or with the older pushState style).. when they're good, blink marks it as a soft nav. There's two intents to expose this concept to the perf timeline.
And there's instrumentation behind all this. It appears as though we may have everything we need to support this in lighthouse! This'd definitely improve our timespan story.
so.. we should see trace events for post-softnav LCP candidates.. I see some CLs that suggest FP, FCP are affected as well.
- Add SoftNavigationHeuristics traces (Ifc8253db) and here's trace events for the heuristics individually. and the final determination. I'm not sure if the timestamp of this last event is meaningful tho.
This is behind --enable-blink-features=SoftNavigationHeuristics or just the blanket--enable-experimental-web-platform-features. I successfully saw the "A soft navigation has been detected" console message with the latter flag on https://next-movies-zeta.vercel.app/
In feb 2023 https://chromium-review.googlesource.com/c/chromium/src/+/4230572 landed, adding this: {type: 'largest-contentful-paint', includeSoftNavigationObservations: true}
this might affect trace event emitting in softnav cases.
Source: GoogleChrome/lighthouse