lighthouse-audit.ts

import { Config, Flags, RunnerResult } from "lighthouse";
import lighthouse from "lighthouse/core/index.cjs";

// See https://github.com/GoogleChrome/lighthouse and https://github.com/GoogleChrome/lighthouse/blob/main/docs/readme.md
export interface LighthouseResult {
  runnerResult: RunnerResult;
  categoriesResult: LighthouseCategoriesResult;
}

export interface LighthouseCategoriesResult {
  accessibilityScore: number;
  performanceScore: number;
  bestPracticesScore: number;
  seoScore: number;
}

export interface LighthouseAuditOptions {
  url: string;
  remoteDebuggingPort: number;
  viewportWidth: number;
  viewportHeight: number;
}

export async function lighthouseAuditAsync(
  lighthouseAuditOptions: LighthouseAuditOptions,
): Promise<LighthouseResult> {
  const options: Flags = {
    onlyCategories: ["accessibility", "performance", "best-practices", "seo"],
    output: "html",
    port: lighthouseAuditOptions.remoteDebuggingPort,
  };
  const config: Config = {
    // see https://github.com/GoogleChrome/lighthouse/blob/main/docs/configuration.md
    extends: "lighthouse:default",
    settings: {
      formFactor: "desktop",
      disableFullPageScreenshot: true,
      throttling: {
        // disable any network or cpu throttling from the default config
        // see https://github.com/GoogleChrome/lighthouse/blob/main/docs/throttling.md
        rttMs: 0,
        throughputKbps: 0,
        cpuSlowdownMultiplier: 1,
        requestLatencyMs: 0,
        downloadThroughputKbps: 0,
        uploadThroughputKbps: 0,
      },
      screenEmulation: {
        // see https://github.com/GoogleChrome/lighthouse/blob/main/docs/emulation.md
        mobile: false,
        width: lighthouseAuditOptions.viewportWidth,
        height: lighthouseAuditOptions.viewportHeight,
        deviceScaleFactor: 1,
      },
    },
  };
  const runnerResult = await lighthouse(
    lighthouseAuditOptions.url,
    options,
    config,
  );
  if (typeof runnerResult === "undefined") {
    // prettier-ignore
    const errorMessage = "Failed to produce lighthouse report. RunnerResult was undefined.";
    throw new Error(errorMessage);
  }

  const lhr = runnerResult.lhr;
  const accessibilityScore = lhr.categories["accessibility"].score ?? 0;
  const performanceScore = lhr.categories["performance"].score ?? 0;
  const bestPracticesScore = lhr.categories["best-practices"].score ?? 0;
  const seoScore = lhr.categories["seo"].score ?? 0;
  const categoriesResult: LighthouseCategoriesResult = {
    // results are from 0 to 1 meaning 0 to 100 percent, applying scale to make it more obvious
    accessibilityScore: accessibilityScore * 100,
    bestPracticesScore: bestPracticesScore * 100,
    performanceScore: performanceScore * 100,
    seoScore: seoScore * 100,
  };
  const runResult: LighthouseResult = {
    runnerResult,
    categoriesResult,
  };
  return runResult;
}