feat(browser): Report web vitals for bfcache restores - #23750
Open
logaretm wants to merge 1 commit into
Open
Conversation
logaretm
force-pushed
the
awad/bfcache-web-vitals
branch
from
August 31, 2026 16:03
c306449 to
b172bce
Compare
Contributor
size-limit report 📦
|
logaretm
force-pushed
the
awad/bfcache-web-vitals
branch
from
September 8, 2026 14:56
b172bce to
89498ab
Compare
logaretm
force-pushed
the
awad/bfcache-web-vitals
branch
from
September 8, 2026 14:57
89498ab to
00a507c
Compare
logaretm
force-pushed
the
awad/bfcache-web-vitals
branch
from
September 9, 2026 13:56
00a507c to
9e62164
Compare
logaretm
force-pushed
the
awad/bfcache-web-vitals
branch
from
September 9, 2026 16:06
9e62164 to
2bfb452
Compare
logaretm
marked this pull request as ready for review
September 9, 2026 16:08
logaretm
requested review from
Lms24 and
msonnb
and removed request for
a team
September 9, 2026 16:08
logaretm
force-pushed
the
awad/bfcache-web-vitals
branch
from
September 9, 2026 16:25
2bfb452 to
aabc750
Compare
logaretm
force-pushed
the
awad/bfcache-web-vitals
branch
from
September 9, 2026 16:28
aabc750 to
1689dad
Compare
logaretm
force-pushed
the
awad/bfcache-web-vitals
branch
from
September 9, 2026 16:40
1689dad to
7e70c6c
Compare
logaretm
force-pushed
the
awad/bfcache-web-vitals
branch
from
September 9, 2026 17:09
7e70c6c to
af8c52d
Compare
logaretm
force-pushed
the
awad/bfcache-web-vitals
branch
from
September 9, 2026 17:32
af8c52d to
9cff25a
Compare
logaretm
force-pushed
the
awad/bfcache-web-vitals
branch
from
September 9, 2026 17:37
9cff25a to
35ba3f5
Compare
logaretm
force-pushed
the
awad/bfcache-web-vitals
branch
from
September 9, 2026 17:52
35ba3f5 to
b201558
Compare
logaretm
force-pushed
the
awad/bfcache-web-vitals
branch
from
September 9, 2026 19:22
b201558 to
dffc394
Compare
logaretm
force-pushed
the
awad/bfcache-web-vitals
branch
from
September 9, 2026 19:26
dffc394 to
bd52ab7
Compare
There was a problem hiding this comment.
Cursor Bugbot has reviewed your changes and found 1 potential issue.
❌ Bugbot Autofix is OFF. To automatically fix reported issues with cloud agents, enable autofix in the Cursor dashboard.
Reviewed by Cursor Bugbot for commit dffc394. Configure here.
|
|
||
| if (reportBfcache) { | ||
| enableBfcacheReporting(); | ||
| } |
There was a problem hiding this comment.
Bfcache opt-in runs too late
Medium Severity
enableBfcacheReporting is only called from webVitalsIntegration setup, but that integration is auto-registered in browserTracingIntegration afterAllSetup. Replay can instrument observers first and pin reportAllChanges on, so incremental LCP and CLS updates each emit a span on the per-navigation path.
Reviewed by Cursor Bugbot for commit dffc394. Configure here.
logaretm
force-pushed
the
awad/bfcache-web-vitals
branch
from
September 9, 2026 19:38
bd52ab7 to
85494a6
Compare
… dropped
`withoutBfcache` dropped every metric web-vitals reported after a
back/forward-cache restore. That was the right call while there was
nothing to attach them to: a restore reuses the frozen document, so the
values would have landed on the span the page had before it was frozen.
Now that a restore gets its own navigation span, they have a correct
parent, so the drop becomes an option rather than a hard rule:
webVitals: { bfcache: true }
Off by default. A restore is near-instant, so its vitals are a different
population from page load vitals, and the earlier concern about skewing
aggregates still applies to anyone who has not decided how to treat them.
`browser.navigation.type: bfcache` makes them separable once enabled.
Reporting per navigation rather than per page load is now what the
tracker flag means, since bfcache restores need it for the same reason
soft navigations do. `reportAllChanges` is switched off for either, since
the per-navigation path relies on each reported value already being final
for its navigation.
Verified end to end in Chrome 152: a restore emits LCP and CLS parented
to the bfcache navigation span on the restore's own trace, and a
bfcache-ineligible back navigation still falls back to a page load.
logaretm
force-pushed
the
awad/bfcache-web-vitals
branch
from
September 9, 2026 23:06
85494a6 to
b6e2c34
Compare
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
1 participant
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Reports web vitals for back/forward cache restores, which we dropped outright before.
Now that a restore gets its own navigation span in #23748, the vitals have a correct parent, so the hardcoded
withoutBfcachedrop becomeswebVitals: { bfcache: true }. Off by default, since a restore is a different population from a page load.Stacked on #23748.