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Cap INP breakdowns to INP duration #528

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Cap INP breakdowns to INP duration #528

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1c332a0
Cap INP breakdowns to INP duration
tunetheweb Aug 30, 2024
677cf8e
Better implementation
tunetheweb Aug 30, 2024
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14 changes: 12 additions & 2 deletions src/attribution/onINP.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -239,10 +239,16 @@ const getIntersectingLoAFs = (

const attributeINP = (metric: INPMetric): INPMetricWithAttribution => {
const firstEntry = metric.entries[0];
const inpTime = firstEntry.startTime + metric.value;
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Nit: just call it endTime or something

const group = entryToEntriesGroupMap.get(firstEntry)!;

const processingStart = firstEntry.processingStart;
const processingEnd = group.processingEnd;
// processingEnd can extend beyond duration for modals where we artificially
// mark event timing duration as that paint.
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Nit: "as that paint" comment is confusing (there is no actual paint)

Perhaps just "where duration ends at the time modal dialog started (and provided visual feedback)"

// See: https://github.com/GoogleChrome/web-vitals/issues/492
// So cap to the INP value.
const processingEnd =
group.processingEnd >= inpTime ? inpTime : group.processingEnd;

// Sort the entries in processing time order.
const processedEventEntries = group.entries.sort((a, b) => {
Expand Down Expand Up @@ -274,6 +280,10 @@ const attributeINP = (metric: INPMetric): INPMetricWithAttribution => {
);

const nextPaintTime = Math.max.apply(Math, nextPaintTimeCandidates);
// If processingEnd has been capped to inpTime then presentationDelay is 0
// Else use the nextPaintTime
const presentationDelay =
processingEnd == inpTime ? 0 : Math.max(nextPaintTime - processingEnd, 0);
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I think this is a fine temporary solution, but, consider just creating a variable such as "used_fallback_time", set up top when endTime < processingEnd, and re-use that everywhere.

(The goal is to expose a clue to event timing for this value, eventually.)

BTW the case where endTime is rounded to within 8ms of processingEnd is almost always another "used_fallback_time" example (i.e. when we actually dont have a paint)


const attribution: INPAttribution = {
interactionTarget: getSelector(interactionTargetElement),
Expand All @@ -285,7 +295,7 @@ const attributeINP = (metric: INPMetric): INPMetricWithAttribution => {
longAnimationFrameEntries: longAnimationFrameEntries,
inputDelay: processingStart - firstEntry.startTime,
processingDuration: processingEnd - processingStart,
presentationDelay: Math.max(nextPaintTime - processingEnd, 0),
presentationDelay: presentationDelay,
loadState: getLoadState(firstEntry.startTime),
};

Expand Down