Lighthouse Playwright - NPM Package

Lighthouse is a tool developed by Google that analyzes web apps and web pages, collecting modern performance metrics and insights on developer best practices.

Playwright is a Node library to automate Chromium, Firefox and WebKit with a single API. Playwright is built to enable cross-browser web automation that is ever-green, capable, reliable and fast.

The purpose of this package is to produce web audit report for several pages in connected mode and in an automated (programmatic) way.

Usage

Installation

You can add the playwright-lighthouse library as a dependency (or dev-dependency) in your project

$ yarn add -D playwright-lighthouse
# or
$ npm install --save-dev playwright-lighthouse

In your code

After completion of the Installation, you can use playwright-lighthouse in your code to audit the current page.

In your test code you need to import playwright-lighthouse and assign a port for the lighthouse scan. You can choose any non-allocated port.

const { playAudit } = require('playwright-lighthouse');
const playwright = require('playwright');

describe('audit example', () => {
  it('open browser', async () => {
    const browser = await playwright['chromium'].launch({
      args: ['--remote-debugging-port=9222'],
    });
    const page = await browser.newPage();
    await page.goto('https://angular.io/');

    await playAudit({
      page: page,
      port: 9222,
    });

    await browser.close();
  });
});

Thresholds per tests

If you don't provide any threshold argument to the playAudit command, the test will fail if at least one of your metrics is under 100.

You can make assumptions on the different metrics by passing an object as argument to the playAudit command:

const { playAudit } = require('playwright-lighthouse');
const playwright = require('playwright');

describe('audit example', () => {
  it('open browser', async () => {
    const browser = await playwright['chromium'].launch({
      args: ['--remote-debugging-port=9222'],
    });
    const page = await browser.newPage();
    await page.goto('https://angular.io/');

    await playAudit({
      page: page,
      thresholds: {
        performance: 50,
        accessibility: 50,
        'best-practices': 50,
        seo: 50,
        pwa: 50,
      },
      port: 9222,
    });

    await browser.close();
  });
});

If the Lighthouse analysis returns scores that are under the one set in arguments, the test will fail.

You can also make assumptions only on certain metrics. For example, the following test will only verify the "correctness" of the performance metric:

await playAudit({
  page: page,
  thresholds: {
    performance: 85,
  },
  port: 9222,
});

This test will fail only when the performance metric provided by Lighthouse will be under 85.

Passing different Lighthouse config to playwright-lighthouse directly

You can also pass any argument directly to the Lighthouse module using the second and third options of the command:

const thresholdsConfig = {
  /* ... */
};

const lighthouseOptions = {
  /* ... your lighthouse options */
};

const lighthouseConfig = {
  /* ... your lighthouse configs */
};

await playAudit({
  thresholds: thresholdsConfig,
  opts: lighthouseOptions,
  config: lighthouseConfig,

  /* ... other configurations */
});

Sometimes it's important to pass a parameter disableStorageReset as false. You can easily make it like this:

    const opts = {
      disableStorageReset: false,
    };

    await playAudit({
      page,
      port: 9222,
      opts,
    });

Generating audit reports

playwright-lighthouse library can produce Lighthouse CSV, HTML and JSON audit reports, that you can host in your CI server. These reports can be useful for ongoing audits and monitoring from build to build.

await playAudit({
  /* ... other configurations */

  reports: {
    formats: {
      json: true, //defaults to false
      html: true, //defaults to false
      csv: true //defaults to false
    },
    name: `name-of-the-report`, //defaults to `lighthouse-${new Date().getTime()}`
    directory:  `path/to/directory`, //defaults to `${process.cwd()}/lighthouse`
  },
});

Sample HTML report:

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- Copyright © 2020- Abhinaba Ghosh