Simulated throttling edge-case: doesn't account for timeout #16588
Description
FAQ
- [-] Yes, my issue is not about variability or throttling.
Note: Didn't find a place to report simulation edge-case scenarios in doc above. - Yes, my issue is not about a specific accessibility audit (file with axe-core instead).
- Yes, my issue is not answered by other FAQs.
URL
https://1um.github.io/lcp-test/lcp-1?fetchCount=40
What happened?
Setup:
Page is shown after timeout or all requests are finished (whatever first).
As fetchCount goes up, LCP is going up, in simulated mode.
Real world scenario:
A/B testing script hides page and apply changes before user sees the original (prevent flicking).
If timeout reached, regardless of a/b test, hydration, etc queries, show page as is.
What did you expect?
LCP is not going up and capped, due to timeout branch.
What have you tried?
Created minimalistic demo of the issue, to rule out any other variables.
| Scenario | URL | Simulated LCP | DevTools LCP |
|---|---|---|---|
| No script | https://1um.github.io/lcp-test/lcp-1?exitEarly=true | 0.9 s | 0.8 s |
| fetchCount=1 | https://1um.github.io/lcp-test/lcp-1?fetchCount=1 | 1.7 s | 1.4 s |
| fetchCount=40 | https://1um.github.io/lcp-test/lcp-1?fetchCount=40 | 3.2 s | 1.7 s |
| fetchCount=100 | https://1um.github.io/lcp-test/lcp-1?fetchCount=100 | 6.3 s | 1.8 s |
| fetchCount=200 | https://1um.github.io/lcp-test/lcp-1?fetchCount=200 | 11.4 s | 1.8 s |
Simulated:
DevTools:
Code:
https://github.com/1um/lcp-test/blob/main/lcp-1.html
How were you running Lighthouse?
Chrome DevTools
Lighthouse Version
12.6.0
Chrome Version
138.0.0.0
Node Version
No response
OS
MacOS