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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,108 @@ | ||
| /** | ||
| * @license | ||
| * Copyright 2024 Google LLC | ||
| * SPDX-License-Identifier: Apache-2.0 | ||
| */ | ||
|
|
||
| import * as Lantern from '../types/lantern.js'; | ||
| import {Metric} from '../metric.js'; | ||
| import {LighthouseError} from '../../../lib/lh-error.js'; | ||
| import {FirstContentfulPaint} from './first-contentful-paint.js'; | ||
|
|
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| /** @typedef {import('../base-node.js').Node} Node */ | ||
|
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| class LargestContentfulPaint extends Metric { | ||
| /** | ||
| * @return {LH.Gatherer.Simulation.MetricCoefficients} | ||
| */ | ||
| static get COEFFICIENTS() { | ||
| return { | ||
| intercept: 0, | ||
| optimistic: 0.5, | ||
| pessimistic: 0.5, | ||
| }; | ||
| } | ||
|
|
||
| /** | ||
| * Low priority image nodes are usually offscreen and very unlikely to be the | ||
| * resource that is required for LCP. Our LCP graphs include everything except for these images. | ||
| * | ||
| * @param {Node} node | ||
| * @return {boolean} | ||
| */ | ||
| static isNotLowPriorityImageNode(node) { | ||
| if (node.type !== 'network') return true; | ||
| const isImage = node.record.resourceType === 'Image'; | ||
| const isLowPriority = node.record.priority === 'Low' || node.record.priority === 'VeryLow'; | ||
| return !isImage || !isLowPriority; | ||
| } | ||
|
|
||
| /** | ||
| * @param {Node} dependencyGraph | ||
| * @param {LH.Artifacts.ProcessedNavigation} processedNavigation | ||
| * @return {Node} | ||
| */ | ||
| static getOptimisticGraph(dependencyGraph, processedNavigation) { | ||
| const lcp = processedNavigation.timestamps.largestContentfulPaint; | ||
| if (!lcp) { | ||
| throw new LighthouseError(LighthouseError.errors.NO_LCP); | ||
| } | ||
|
|
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| return FirstContentfulPaint.getFirstPaintBasedGraph(dependencyGraph, { | ||
| cutoffTimestamp: lcp, | ||
| treatNodeAsRenderBlocking: LargestContentfulPaint.isNotLowPriorityImageNode, | ||
| }); | ||
| } | ||
|
|
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| /** | ||
| * @param {Node} dependencyGraph | ||
| * @param {LH.Artifacts.ProcessedNavigation} processedNavigation | ||
| * @return {Node} | ||
| */ | ||
| static getPessimisticGraph(dependencyGraph, processedNavigation) { | ||
| const lcp = processedNavigation.timestamps.largestContentfulPaint; | ||
| if (!lcp) { | ||
| throw new LighthouseError(LighthouseError.errors.NO_LCP); | ||
| } | ||
|
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| return FirstContentfulPaint.getFirstPaintBasedGraph(dependencyGraph, { | ||
| cutoffTimestamp: lcp, | ||
| treatNodeAsRenderBlocking: _ => true, | ||
| // For pessimistic LCP we'll include *all* layout nodes | ||
| additionalCpuNodesToTreatAsRenderBlocking: node => node.didPerformLayout(), | ||
| }); | ||
| } | ||
|
|
||
| /** | ||
| * @param {LH.Gatherer.Simulation.Result} simulationResult | ||
| * @return {LH.Gatherer.Simulation.Result} | ||
| */ | ||
| static getEstimateFromSimulation(simulationResult) { | ||
| const nodeTimesNotOffscreenImages = Array.from(simulationResult.nodeTimings.entries()) | ||
| .filter(entry => LargestContentfulPaint.isNotLowPriorityImageNode(entry[0])) | ||
| .map(entry => entry[1].endTime); | ||
|
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| return { | ||
| timeInMs: Math.max(...nodeTimesNotOffscreenImages), | ||
| nodeTimings: simulationResult.nodeTimings, | ||
| }; | ||
| } | ||
|
|
||
| /** | ||
| * @param {Lantern.Simulation.MetricComputationDataInput} data | ||
| * @param {Omit<import('../metric.js').Extras, 'optimistic'>=} extras | ||
| * @return {Promise<LH.Artifacts.LanternMetric>} | ||
| */ | ||
| static async compute(data, extras) { | ||
| const fcpResult = extras?.fcpResult; | ||
| if (!fcpResult) { | ||
| throw new Error('FCP is required to calculate the LCP metric'); | ||
| } | ||
|
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| const metricResult = await super.compute(data, extras); | ||
| metricResult.timing = Math.max(metricResult.timing, fcpResult.timing); | ||
| return metricResult; | ||
| } | ||
| } | ||
|
|
||
| export {LargestContentfulPaint}; |
24 changes: 11 additions & 13 deletions
24
.../lantern-largest-contentful-paint-test.js → .../lantern-largest-contentful-paint-test.js
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