Puppeteer Top 50 Interview Questions and Answers

Learn and master Puppeteer with Top 30 Interview Questions and Answers often asked in technical interviews.

1. What is Puppeteer?
   
   Puppeteer is a Node.js library developed by Google that provides a high-level API for controlling headless Chrome or Chromium browsers. It allows you to automate browser actions such as navigation, form submission, DOM manipulation, and more.
   
2. How do you install Puppeteer?
   
   Puppeteer can be installed via npm, the Node.js package manager, using the following command:

npm install puppeteer

3. How do you launch a browser using Puppeteer?
   
   To launch a browser instance using Puppeteer, you can use the puppeteer.launch() method. Here’s an example:

const puppeteer = require('puppeteer');

(async () => {
  const browser = await puppeteer.launch();
  // Rest of your code
})();

4. How do you open a new page in Puppeteer?
   
   To open a new page in Puppeteer, you can use the browser.newPage() method. Here’s an example:

const page = await browser.newPage();

5. How do you navigate to a URL using Puppeteer?
   
   To navigate to a specific URL using Puppeteer, you can use the page.goto() method. Here’s an example:

await page.goto('https://www.example.com');

6. How do you wait for a specific element to appear on the page in Puppeteer?
   
   To wait for a specific element to appear on the page in Puppeteer, you can use the page.waitForSelector() method. Here’s an example:

await page.waitForSelector('#myElement');

7. How do you click on an element in Puppeteer?
   
   To click on an element in Puppeteer, you can use the page.click() method. Here’s an example:

await page.click('#myButton');

8. How do you fill out a form in Puppeteer?
   
   To fill out a form in Puppeteer, you can use the page.type() method. Here’s an example:

await page.type('#username', 'john_doe');
await page.type('#password', 'password123');

9. How do you take a screenshot using Puppeteer?
   
   To take a screenshot of a page using Puppeteer, you can use the page.screenshot() method. Here’s an example:

await page.screenshot({ path: 'screenshot.png' });

10. How do you interact with dropdown menus in Puppeteer?
    
    To interact with dropdown menus in Puppeteer, you can use the page.select() method. Here’s an example:

await page.select('#myDropdown', 'optionValue');

11. How do you extract data from the page using Puppeteer?
    
    To extract data from the page using Puppeteer, you can use various methods like page.evaluate(), page.$eval(), or page.$$eval(). Here’s an example using page.evaluate():

const pageTitle = await page.evaluate(() => document.title);

12. How do you handle navigation events in Puppeteer?
    
    To handle navigation events in Puppeteer, you can use the page.on('navigation') event. Here’s an example:

page.on('navigation', (event) => {
  console.log('Navigating to:', event.url);
});

13. How do you interact with checkboxes in Puppeteer?
    
    To interact with checkboxes in Puppeteer, you can use the page.check() or page.uncheck() methods. Here’s an example:

await page.check('#myCheckbox');

14. How do you extract the text content of an element in Puppeteer?
    
    To extract the text content of an element in Puppeteer, you can use the page.$eval() method. Here’s an example:

const elementText = await page.$eval('#myElement', (element) => element.textContent);

15. How do you handle popup dialogs in Puppeteer?
    
    To handle popup dialogs in Puppeteer, you can use the page.on('dialog') event. Here’s an example:

page.on('dialog', async (dialog) => {
  console.log('Dialog message:', dialog.message());
  await dialog.dismiss();
});

16. How do you emulate a mobile device using Puppeteer?
    
    To emulate a mobile device using Puppeteer, you can use the page.emulate() method. Here’s an example:

await page.emulate(puppeteer.devices['iPhone X']);

17. How do you wait for a specific condition to be fulfilled in Puppeteer?
    
    To wait for a specific condition to be fulfilled in Puppeteer, you can use the page.waitForFunction() method. Here’s an example:

await page.waitForFunction(() => document.querySelector('#myElement').classList.contains('active'));

18. How do you intercept and modify network requests in Puppeteer?
    
    To intercept and modify network requests in Puppeteer, you can use the page.setRequestInterception() method and the request.continue() or request.respond() methods.
    
    Here’s an example:

await page.setRequestInterception(true);

page.on('request', (request) => {
  if (request.url().endsWith('.png')) {
    request.respond({ body: 'Hello, Puppeteer!' });
  } else {
    request.continue();
  }
});

19. How do you authenticate with a username and password using Puppeteer?
    
    To authenticate with a username and password using Puppeteer, you can use the page.authenticate() method. Here’s an example:

await page.authenticate({ username: 'john_doe', password: 'password123' });

20. How do you generate a PDF from a page using Puppeteer?
    
    To generate a PDF from a page using Puppeteer, you can use the page.pdf() method. Here’s an example:

await page.pdf({ path: 'output.pdf' });

21. How do you handle page errors in Puppeteer?
    
    To handle page errors in Puppeteer, you can use the page.on('error') event. Here’s an example:

page.on('error', (error) => {
  console.error('Page error:', error);
});

22. How do you handle page console messages in Puppeteer?
    
    To handle page console messages in Puppeteer, you can use the page.on('console') event. Here’s an example:

page.on('console', (message) => {
  console.log('Console message:', message.text());
});

23. How do you set and get cookies in Puppeteer?
    
    To set and get cookies in Puppeteer, you can use the page.setCookie() and page.cookies() methods. Here’s an example:

await page.setCookie({ name: 'session', value: 'abc123' });
const cookies = await page.cookies();

24. How do you handle file downloads in Puppeteer?
    
    To handle file downloads in Puppeteer, you can use the page._client.send() method. Here’s an example:

page._client.send('Page.setDownloadBehavior', { behavior: 'allow', downloadPath: '/path/to/downloads' });

25. How do you evaluate JavaScript code within the context of a page in Puppeteer?
    
    To evaluate JavaScript code within the context of a page in Puppeteer, you can use the page.evaluate() method. Here’s an example:

const result = await page.evaluate(() => {
  return 2 + 2;
});
console.log('Result:', result);

26. How do you handle frames and iframes in Puppeteer?
    
    To handle frames and iframes in Puppeteer, you can use the page.frames() method to access frame objects. Here’s an example:

const frame = page.frames()[0];

27. How do you handle page timeouts in Puppeteer?
    
    To handle page timeouts in Puppeteer, you can use the page.setDefaultTimeout() method. Here’s an example:

page.setDefaultTimeout(5000); // 5 seconds

28. How do you set viewport size in Puppeteer?
    
    To set the viewport size in Puppeteer, you can use the page.setViewport() method. Here’s an example:

await page.setViewport({ width: 1280, height: 720 });

29. How do you handle page navigation errors in Puppeteer?
    
    To handle page navigation errors in Puppeteer, you can use the page.on('pageerror') event. Here’s an example:

page.on('pageerror', (error) => {
  console.error('Page navigation error:', error);
});

30. How do you close the browser instance in Puppeteer?
    
    To close the browser instance in Puppeteer, you can use the browser.close() method. Here’s an example:

await browser.close();

31. How do you handle browser navigation errors in Puppeteer?

To handle browser navigation errors in Puppeteer, you can use the page.on('error') event. Here’s an example:

page.on('error', (err) => {
  console.error('Navigation error:', err);
});

32. How do you wait for a page to fully load in Puppeteer?

To wait for a page to fully load in Puppeteer, you can use the page.waitForNavigation() method. Here’s an example:

await page.goto('https://www.example.com');
await page.waitForNavigation();

33. How do you clear browser cookies in Puppeteer?

To clear browser cookies in Puppeteer, you can use the page.deleteCookie() method. Here’s an example:

await page.deleteCookie({ name: 'session' });

34. How do you emulate different devices with specific screen sizes in Puppeteer?

To emulate different devices with specific screen sizes in Puppeteer, you can use the page.setViewport() method. Here’s an example:

await page.setViewport({ width: 375, height: 812, deviceScaleFactor: 2 });

35. How do you handle basic authentication prompts in Puppeteer?

To handle basic authentication prompts in Puppeteer, you can use the page.authenticate() method. Here’s an example:

await page.authenticate({ username: 'username', password: 'password' });

36. How do you handle file uploads in Puppeteer?

To handle file uploads in Puppeteer, you can use the page.setFileChooserIntercepted() method.

Here’s an example:

page.on('filechooser', async (fileChooser) => {
  await fileChooser.accept(['/path/to/file.txt']);
});

37. How do you simulate keyboard inputs in Puppeteer?

To simulate keyboard inputs in Puppeteer, you can use the page.keyboard.type() method. Here’s an example:

await page.focus('#myInput');
await page.keyboard.type('Hello, Puppeteer!');

38. How do you handle page timeouts and set custom timeout values in Puppeteer?

To handle page timeouts and set custom timeout values in Puppeteer, you can use the page.setDefaultTimeout() method.

Here’s an example:

page.setDefaultTimeout(10000); // 10 seconds

39. How do you handle slow network conditions in Puppeteer?

To simulate slow network conditions in Puppeteer, you can use the page.setOfflineMode() method. Here’s an example:

await page.setOfflineMode(true);

40. How do you handle page navigation events in Puppeteer?

To handle page navigation events in Puppeteer, you can use the page.on('framenavigated') event. Here’s an example:

page.on('framenavigated', (frame) => {
  console.log('Frame navigated to:', frame.url());
});

41. How do you extract the value of an attribute from an element in Puppeteer?

To extract the value of an attribute from an element in Puppeteer, you can use the page.$eval() method. Here’s an example:

const elementAttributeValue = await page.$eval('#myElement', (element) => element.getAttribute('data-value'));

42. How do you handle geolocation prompts in Puppeteer?

To handle geolocation prompts in Puppeteer, you can use the page.setGeolocation() method. Here’s an example:

await page.setGeolocation({ latitude: 37.7749, longitude: -122.4194 });

43. How do you scroll to a specific element on a page in Puppeteer?

To scroll to a specific element on a page in Puppeteer, you can use the page.$eval() method along with the scrollIntoView() method. Here’s an example:

await page.$eval('#myElement', (element) => element.scrollIntoView());

44. How do you handle page geolocation permission prompts in Puppeteer?

To handle page geolocation permission prompts in Puppeteer, you can use the page.setGeolocationOverride() method. Here’s an example:

await page.setGeolocationOverride({ latitude: 37.7749, longitude: -122.4194, accuracy: 100 });

45. How do you execute JavaScript code within the context of a page in Puppeteer?

To execute JavaScript code within the context of a page in Puppeteer, you can use the page.evaluate() method.

Here’s an example:

const pageTitle = await page.evaluate(() => document.title);

46. How do you handle page crashes in Puppeteer?

To handle page crashes in Puppeteer, you can use the page.on('crash') event. Here’s an example:

page.on('crash', () => {
  console.error('Page crashed!');
});

47. How do you handle keyboard shortcuts in Puppeteer?
To handle keyboard shortcuts in Puppeteer, you can use the page.keyboard.down() and page.keyboard.up() methods.

Here’s an example:

await page.keyboard.down('Control');
await page.keyboard.press('KeyC');
await page.keyboard.up('Control');

48. How do you handle page resource errors in Puppeteer?

To handle page resource errors in Puppeteer, you can use the page.on('requestfailed') event. Here’s an example:

page.on('requestfailed', (request) => {
  console.error('Resource failed to load:', request.url());
});

49. How do you simulate touch events in Puppeteer?

To simulate touch events in Puppeteer, you can use the page.touchscreen.tap() method. Here’s an example:

await page.touchscreen.tap(100, 100);

50. How do you intercept and modify WebSocket messages in Puppeteer?

To intercept and modify WebSocket messages in Puppeteer, you can use the page.on('websocket') event.

Here’s an example:

page.on('websocket', (websocket) => {
  websocket.on('message', (message) => {
    console.log('WebSocket message:', message);
  });
});