On Mon, Mar 9, 2026, 6:53 PM Alex Russell <[email protected]> wrote:

> I would hope that all forced layouts that generate long jank
> (`getComptuedStyle()` in Noam's example) would generate these events. Is
> there reason to believe they would/should not?


They all do, but there is no distinction between time spent in style vs
layout computation. This is a problem of missing attribution, the time
spent in "style and layout" seems like a big opaque purple box that
developers cannot influence or understand.


> Best,
>
> Alex
>
> On Monday, March 9, 2026 at 5:30:17 AM UTC-7 Noam Rosenthal wrote:
>
>> On Mon, Mar 9, 2026 at 3:37 AM Yoav Weiss (@Shopify)
>> <[email protected]> wrote:
>> >
>> >
>> >
>> > On Friday, March 6, 2026 at 6:42:41 PM UTC+1 Ian Kilpatrick wrote:
>> >
>> >
>> >
>> > On Fri, Mar 6, 2026 at 9:38 AM Ian Kilpatrick <[email protected]>
>> wrote:
>> >
>> > Hmm... this is pretty fragile, e.g. you are missing the interleaving
>> that occurs for anchor-positioning for example.
>> >
>> https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/core/css/style_engine.cc;l=3896;drc=4ae3a738cbcbfb87d2bf747e530650484e448361;bpv=1;bpt=1
>> >
>> >
>> > Fair. Does that mean that these style and layout calcs are not
>> accounted for in the current probes? are they accounted from in the current
>> LoAF implementation?
>>
>> Currently, LoAF cares about two things:
>> - The "lifecycle" style-and-layout timestamp, which is a well defined
>> time within the rendering cycle, regardless of whether more
>> style/layout happens afterwards.
>> - Forced style and layout, as one bucket, when called from a JS method
>> that needs a synchronous result that depends on up to date values.
>>
>> Where I would draw the line between style and layout depends on
>> whether the methods would be called for `getComputedStyle()` or only
>> if a measurement like `offsetLeft` is required.
>> I don't know what the answer for that when anchor position fallbacks are
>> used.
>>
>

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