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docs: document what simulated throttling for soft navigations needs upstream - #25
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…pstream A soft navigation step errors under Lighthouse's default simulated throttling. docs/simulated-throttling.md records why, what was measured on the e2e fixture app once Lantern is given a graph root, and the seven changes Lantern and Lighthouse need before simulate can work for a soft navigation. Linked from the upstreaming doc, the package README and the Throttling guide.
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Closes #24. Background for #23.
What
A new
docs/simulated-throttling.md:What happens today. Under
simulate, seven audits of a soft navigation step error withrootRequest not foundand the Performance score isnull. Lantern'sPageDependencyGraph.createGraphroots its graph at the document request, and a soft navigation has none.Why a root is not enough. I gave Lantern a root on the e2e fixture app, a cached document request at
SoftNavigationStart, and compared the result with the same soft navigation under DevTools throttling:Three rules in Lantern explain it: the FCP graph leaves out the
fetchthe paint waited for, a request that waits for another is simulated next to it, and every origin is charged a new connection.What has to change. Seven changes with their files: four in Lantern (Chrome DevTools frontend), three in Lighthouse, and the order they make sense in.
Until then. The package keeps requiring
devtoolsorprovided. The options for a bridge are in Simulated throttling for soft navigation steps: land it upstream or bridge it in the package #23.Limits of the measurement. One small app, two runs, one machine.
It is linked from
docs/upstreaming-to-lighthouse.md(where it explains why the step passesthrottlingMethod, and as a new open question), from the Throttling section of the package README and from the Throttling guide of the docs site.Verified
@paulirish/trace_engine0.0.67 and Chrome 157. The scripts are in Simulated throttling for soft navigation steps: land it upstream or bridge it in the package #23.ChromeDevTools/devtools-frontendatmain.pnpm nx format:checkandpnpm nx affected -t lint test build typecheckpass. Only Markdown changed.