lighthouseConfig.js

// https://github.com/GoogleChrome/lighthouse/blob/master/lighthouse-core/config/constants.js
/**
 * Adjustments needed for DevTools network throttling to simulate
 * more realistic network conditions.
 * @see https://crbug.com/721112
 * @see https://docs.google.com/document/d/10lfVdS1iDWCRKQXPfbxEn4Or99D64mvNlugP1AQuFlE/edit
 */
const DEVTOOLS_RTT_ADJUSTMENT_FACTOR = 3.75;
const DEVTOOLS_THROUGHPUT_ADJUSTMENT_FACTOR = 0.9;

export const throttling = {
  DEVTOOLS_RTT_ADJUSTMENT_FACTOR,
  DEVTOOLS_THROUGHPUT_ADJUSTMENT_FACTOR,
  // These values align with WebPageTest's definition of "Fast 3G"
  // But offer similar charateristics to roughly the 75th percentile of 4G connections.
  mobileSlow4G: {
    rttMs: 150,
    throughputKbps: 1.6 * 1024,
    requestLatencyMs: 150 * DEVTOOLS_RTT_ADJUSTMENT_FACTOR,
    downloadThroughputKbps: 1.6 * 1024 * DEVTOOLS_THROUGHPUT_ADJUSTMENT_FACTOR,
    uploadThroughputKbps: 750 * DEVTOOLS_THROUGHPUT_ADJUSTMENT_FACTOR,
    cpuSlowdownMultiplier: 4,
  },
  // These values partially align with WebPageTest's definition of "Regular 3G".
  // These values are meant to roughly align with Chrome UX report's 3G definition which are based
  // on HTTP RTT of 300-1400ms and downlink throughput of <700kbps.
  mobileRegular3G: {
    rttMs: 300,
    throughputKbps: 700,
    requestLatencyMs: 300 * DEVTOOLS_RTT_ADJUSTMENT_FACTOR,
    downloadThroughputKbps: 700 * DEVTOOLS_THROUGHPUT_ADJUSTMENT_FACTOR,
    uploadThroughputKbps: 700 * DEVTOOLS_THROUGHPUT_ADJUSTMENT_FACTOR,
    cpuSlowdownMultiplier: 4,
  },
  // Using a "broadband" connection type
  // Corresponds to "Dense 4G 25th percentile" in https://docs.google.com/document/d/1Ft1Bnq9-t4jK5egLSOc28IL4TvR-Tt0se_1faTA4KTY/edit#heading=h.bb7nfy2x9e5v
  desktopDense4G: {
    rttMs: 40,
    throughputKbps: 10 * 1024,
    cpuSlowdownMultiplier: 1,
    requestLatencyMs: 0, // 0 means unset
    downloadThroughputKbps: 0,
    uploadThroughputKbps: 0,
  },
};

/**
 * @type {Required<LH.SharedFlagsSettings['screenEmulation']>}
 */
const MOTOG4_EMULATION_METRICS = {
  mobile: true,
  width: 360,
  height: 640,
  // Moto G4 is really 3, but a higher value here works against
  // our perf recommendations.
  // https://github.com/GoogleChrome/lighthouse/issues/10741#issuecomment-626903508
  deviceScaleFactor: 2.625,
  disabled: false,
};

/**
 * Desktop metrics adapted from emulated_devices/module.json
 * @type {Required<LH.SharedFlagsSettings['screenEmulation']>}
 */
const DESKTOP_EMULATION_METRICS = {
  mobile: false,
  width: 1350,
  height: 940,
  deviceScaleFactor: 1,
  disabled: false,
};

const screenEmulationMetrics = {
  mobile: MOTOG4_EMULATION_METRICS,
  desktop: DESKTOP_EMULATION_METRICS,
};

// eslint-disable-next-line max-len
const MOTOG4_USERAGENT =
  'Mozilla/5.0 (Linux; Android 7.0; Moto G (4)) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/90.0.4420.0 Mobile Safari/537.36 Chrome-Lighthouse';
// eslint-disable-next-line max-len
const DESKTOP_USERAGENT =
  'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/90.0.4420.0 Safari/537.36 Chrome-Lighthouse';

const userAgents = {
  mobile: MOTOG4_USERAGENT,
  desktop: DESKTOP_USERAGENT,
};

// https://github.com/GoogleChrome/lighthouse/blob/master/lighthouse-core/config/lr-desktop-config.js
export const desktop = {
  extends: 'lighthouse:default',
  settings: {
    maxWaitForFcp: 15 * 1000,
    maxWaitForLoad: 35 * 1000,
    formFactor: 'desktop',
    throttling: throttling.desktopDense4G,
    screenEmulation: screenEmulationMetrics.desktop,
    emulatedUserAgent: userAgents.desktop,
    // Skip the h2 audit so it doesn't lie to us. See https://github.com/GoogleChrome/lighthouse/issues/6539
    skipAudits: ['uses-http2'],
  },
};

// https://github.com/GoogleChrome/lighthouse/blob/master/lighthouse-core/config/lr-mobile-config.js
export const mobile = {
  extends: 'lighthouse:default',
  settings: {
    maxWaitForFcp: 15 * 1000,
    maxWaitForLoad: 35 * 1000,
    // lighthouse:default is mobile by default
    // Skip the h2 audit so it doesn't lie to us. See https://github.com/GoogleChrome/lighthouse/issues/6539
    skipAudits: ['uses-http2'],
  },
};