@wdio/devtools-service

What is @wdio/devtools-service?

@wdio/devtools-service is a WebdriverIO service that provides integration with Chrome DevTools Protocol. It allows you to use Chrome DevTools features in your WebdriverIO tests, such as capturing performance metrics, taking screenshots, and more.

What are @wdio/devtools-service's main functionalities?

Capturing Performance Metrics

This feature allows you to capture performance metrics such as First Meaningful Paint, DOM Content Loaded, and more. The code sample demonstrates how to capture these metrics for a given URL.

const { remote } = require('webdriverio');
const options = { capabilities: { browserName: 'chrome' } };
(async () => {
  const browser = await remote(options);
  await browser.url('https://example.com');
  const metrics = await browser.getMetrics();
  console.log(metrics);
  await browser.deleteSession();
})();

Taking Screenshots

This feature allows you to take screenshots of the current browser window. The code sample demonstrates how to navigate to a URL and take a screenshot.

const { remote } = require('webdriverio');
const options = { capabilities: { browserName: 'chrome' } };
(async () => {
  const browser = await remote(options);
  await browser.url('https://example.com');
  const screenshot = await browser.takeScreenshot();
  console.log(screenshot);
  await browser.deleteSession();
})();

Network Throttling

This feature allows you to simulate different network conditions. The code sample demonstrates how to throttle the network to simulate a slower connection.

const { remote } = require('webdriverio');
const options = { capabilities: { browserName: 'chrome' } };
(async () => {
  const browser = await remote(options);
  await browser.url('https://example.com');
  await browser.throttle({
    offline: false,
    downloadThroughput: 500 * 1024 / 8,
    uploadThroughput: 500 * 1024 / 8,
    latency: 20
  });
  await browser.deleteSession();
})();

Other packages similar to @wdio/devtools-service

puppeteer

Puppeteer is a Node library which provides a high-level API to control Chrome or Chromium over the DevTools Protocol. It offers similar functionalities such as capturing performance metrics, taking screenshots, and network throttling. However, Puppeteer is more focused on headless browser automation and is not integrated into the WebdriverIO ecosystem.

selenium-webdriver

Selenium WebDriver is a popular tool for automating web applications for testing purposes. While it does not natively support Chrome DevTools Protocol, it can be extended with additional libraries to achieve similar functionalities. Selenium WebDriver is more general-purpose and supports multiple browsers and programming languages.

README

WebdriverIO DevTools Service

A WebdriverIO service that allows you to run Chrome DevTools commands in your tests

With Chrome v63 and up the browser started to support multi clients allowing arbitrary clients to access the Chrome DevTools Protocol. This provides interesting opportunities to automate Chrome beyond the WebDriver protocol. With this service you can enhance the wdio browser object to leverage that access and call Chrome DevTools commands within your tests to e.g. intercept requests, throttle network capabilities or take CSS/JS coverage.

Note: this service currently only supports Chrome v63 and up!

Installation

The easiest way is to keep @wdio/devtools-service as a devDependency in your package.json.

{
  "devDependencies": {
    "@wdio/devtools-service": "^5.0.0"
  }
}

You can simple do it by:

npm install @wdio/devtools-service --save-dev

Instructions on how to install WebdriverIO can be found here.

Configuration

In order to use the service you just need to add the service to your service list in your wdio.conf.js like:

// wdio.conf.js
export.config = {
  // ...
  services: ['devtools'],
  // ...
};

Usage

For now the service allows two different ways to access the Chrome DevTools Protocol:

cdp Command

The cdp command is a custom command added to the browser scope that allows you to call directly commands to the protocol.

browser.cdp(<domain>, <command>, <arguments>)

For example if you want to get the JavaScript coverage of your page you can do the following:

it('should take JS coverage', () => {
    /**
     * enable necessary domains
     */
    browser.cdp('Profiler', 'enable')
    browser.cdp('Debugger', 'enable')

    /**
     * start test coverage profiler
     */
    browser.cdp('Profiler', 'startPreciseCoverage', {
        callCount: true,
        detailed: true
    })

    browser.url('http://google.com')

    /**
     * capture test coverage
     */
    const { result } = browser.cdp('Profiler', 'takePreciseCoverage')
    const coverage = result.filter((res) => res.url !== '')
    console.log(coverage)
})

cdpConnection Command

Returns the host and port the Chrome DevTools interface is connected to.

const connection = browser.cdpConnection()
console.log(connection);  // outputs: { host: 'localhost', port: 50700 }

getNodeId(selector) and getNodeIds(selector) Command

Helper method to get the nodeId of an element in the page. NodeIds are similar like WebDriver node ids an identifier for a node. It can be used as a parameter for other Chrome DevTools methods, e.g. DOM.focus.

const nodeId = browser.getNodeId('body')
console.log(nodeId) // outputs: 4
const nodeId = browser.getNodeIds('img')
console.log(nodeId) // outputs: [ 40, 41, 42, 43, 44, 45 ]

startTracing(categories, samplingFrequency) Command

Start tracing the browser. You can optionally pass in custom tracing categories (defaults to this list) and the sampling frequency (defaults to 10000).

browser.startTracing()

endTracing Command

Stop tracing the browser.

browser.endTracing()

getTraceLogs Command

Returns the tracelogs that was captured within the tracing period. You can use this command to store the trace logs on the file system to analyse the trace via Chrome DevTools interface.

browser.startTracing()
browser.url('http://json.org')
browser.endTracing()

fs.writeFileSync('/path/to/tracelog.json', JSON.stringify(browser.getTraceLogs()))

getSpeedIndex Command

Returns the Speed Index and Perceptual Speed Index from the page load that happened between the tracing period.

browser.startTracing()
browser.url('http://json.org')
browser.endTracing()

console.log(browser.getSpeedIndex())
// outputs
// { speedIndex: 689.6634800064564,
//   perceptualSpeedIndex: 785.0901860232523 }

getPerformanceMetrics Command

Returns an object with a variety of performance metrics.

browser.startTracing()
browser.url('http://json.org')
browser.endTracing()

console.log(browser.getPerformanceMetrics())
// outputs:
// { firstPaint: 621.432,
//   firstContentfulPaint: 621.44,
//   firstMeaningfulPaint: 621.442,
//   domContentLoaded: 474.96,
//   timeToFirstInteractive: 621.442,
//   load: 1148.313 }

getPageWeight Command

Returns page weight information of the last page load.

browser.startTracing()
browser.url('https://webdriver.io')
browser.endTracing()

console.log(browser.getPageWeight())
// outputs:
// { pageWeight: 2438485,
//   transferred: 1139136,
//   requestCount: 72,
//   details: {
//       Document: { size: 221705, encoded: 85386, count: 11 },
//       Stylesheet: { size: 52712, encoded: 50130, count: 2 },
//       Image: { size: 495023, encoded: 482433, count: 36 },
//       Script: { size: 1073597, encoded: 322854, count: 15 },
//       Font: { size: 84412, encoded: 84412, count: 5 },
//       Other: { size: 1790, encoded: 1790, count: 2 },
//       XHR: { size: 509246, encoded: 112131, count: 1 } }
// }

Event Listener

In order to capture events in the browser you can register an event listener to a Chrome DevTools event like:

it('should listen on network events', () => {
    browser.cdp('Network', 'enable')
    browser.on('Network.responseReceived', (params) => {
        console.log(`Loaded ${params.response.url}`)
    })
    browser.url('https://www.google.com')
})

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