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first-contentful-paint.js
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first-contentful-paint.js
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/**
* @license
* Copyright 2018 Google LLC
* SPDX-License-Identifier: Apache-2.0
*/
import {Audit} from '../audit.js';
import * as i18n from '../../lib/i18n/i18n.js';
import {FirstContentfulPaint as ComputedFcp} from '../../computed/metrics/first-contentful-paint.js';
const UIStrings = {
/** Description of the First Contentful Paint (FCP) metric, which marks the time at which the first text or image is painted by the browser. This is displayed within a tooltip when the user hovers on the metric name to see more. No character length limits. The last sentence starting with 'Learn' becomes link text to additional documentation. */
description: 'First Contentful Paint marks the time at which the first text or image is ' +
'painted. [Learn more about the First Contentful Paint metric](https://developer.chrome.com/docs/lighthouse/performance/first-contentful-paint/).',
};
const str_ = i18n.createIcuMessageFn(import.meta.url, UIStrings);
class FirstContentfulPaint extends Audit {
/**
* @return {LH.Audit.Meta}
*/
static get meta() {
return {
id: 'first-contentful-paint',
title: str_(i18n.UIStrings.firstContentfulPaintMetric),
description: str_(UIStrings.description),
scoreDisplayMode: Audit.SCORING_MODES.NUMERIC,
supportedModes: ['navigation'],
requiredArtifacts: ['traces', 'devtoolsLogs', 'GatherContext', 'URL'],
};
}
/**
* @return {{mobile: {scoring: LH.Audit.ScoreOptions}, desktop: {scoring: LH.Audit.ScoreOptions}}}
*/
static get defaultOptions() {
return {
mobile: {
// 25th and 8th percentiles HTTPArchive -> median and p10.
// https://bigquery.cloud.google.com/table/httparchive:lighthouse.2021_05_01_mobile
// see https://www.desmos.com/calculator/6wi8rhipve
scoring: {
p10: 1800,
median: 3000,
},
},
desktop: {
// SELECT QUANTILES(renderStart, 21) FROM [httparchive:summary_pages.2020_07_01_desktop] LIMIT 1000
scoring: {
p10: 934,
median: 1600,
},
},
};
}
/**
* @param {LH.Artifacts} artifacts
* @param {LH.Audit.Context} context
* @return {Promise<LH.Audit.Product>}
*/
static async audit(artifacts, context) {
const trace = artifacts.traces[Audit.DEFAULT_PASS];
const devtoolsLog = artifacts.devtoolsLogs[Audit.DEFAULT_PASS];
const gatherContext = artifacts.GatherContext;
const metricComputationData = {trace, devtoolsLog, gatherContext,
settings: context.settings, URL: artifacts.URL};
const metricResult = await ComputedFcp.request(metricComputationData, context);
const options = context.options[context.settings.formFactor];
return {
score: Audit.computeLogNormalScore(
options.scoring,
metricResult.timing
),
scoringOptions: options.scoring,
numericValue: metricResult.timing,
numericUnit: 'millisecond',
displayValue: str_(i18n.UIStrings.seconds, {timeInMs: metricResult.timing}),
};
}
}
export default FirstContentfulPaint;
export {UIStrings};