20 Puppeteer Interview Questions and Answers

Puppeteer is a tool used by developers to automate web browsers. It is often used for testing web applications and can be used to automate tasks on the web. If you are applying for a position that requires Puppeteer, you may be asked questions about it during your interview. In this article, we will review some of the most common Puppeteer interview questions and how you should answer them.

Puppeteer Interview Questions and Answers

Here are 20 commonly asked Puppeteer interview questions and answers to prepare you for your interview:

1. What is Puppeteer?

Puppeteer is a Node library which provides a high-level API to control Chrome or Chromium over the DevTools Protocol.

2. What are the main features offered by Puppeteer?

The main features offered by Puppeteer are the ability to control and automate Chromium-based browsers, and the ability to take screenshots and create PDFs of web pages.

3. How does Puppeteer differ from Selenium WebDriver?

Puppeteer is a Node.js library that provides a high-level API to control Chrome or Chromium over the DevTools Protocol. Selenium is a Java library that allows you to automate web browser interactions.

4. Can you explain what headless mode means in the context of browser automation?

Headless mode is a way of running a web browser without actually displaying the browser window. This can be useful for running automated tests or for web scraping, where you don’t need to actually see the browser window in order to interact with the page.

5. Is it possible to control Chrome DevTools with Puppeteer? If yes, then how?

Yes, it is possible to control Chrome DevTools with Puppeteer. You can do this by using the Puppeteer API to send commands to the DevTools instance that is attached to the browser.

6. Is there a way to access all frames on a page using Puppeteer? If yes, then how?

Yes, there is a way to access all frames on a page using Puppeteer. You can do this by using the page.frames() method. This will return an array of all the frames on the page, which you can then iterate over and work with as you please.

7. Do you know what CSS selectors and XPath expressions are?

CSS selectors and XPath expressions are both ways of targeting specific elements on a web page in order to interact with them. CSS selectors are usually more concise and easier to read, while XPath expressions can be more powerful but can also be more complex.

8. What do you understand about asynchronous code execution in JavaScript?

Asynchronous code execution in JavaScript means that code can be executed without blocking the main thread. This allows for more efficient code execution, as well as the ability to perform tasks in the background while the main thread is still running.

9. When should you use Promises instead of callbacks?

Promises should be used when you want to make sure that an asynchronous operation has completed before moving on to the next operation. This is especially important when you are chaining together multiple asynchronous operations. Callbacks, on the other hand, can be used when the order of operations is not as important.

10. What’s a practical example of where an async/await pattern can be used?

One practical example of where the async/await pattern can be used is when making requests to a server. If you are making multiple requests to the server, you can use async/await to wait for each request to finish before making the next one. This ensures that you don’t overload the server and can make the most efficient use of your resources.

11. What are the different ways in which we can wait for something to happen while running our tests?

There are a few different ways that we can wait for something to happen while running our tests. We can use the waitFor function to wait for a specific condition to be met, or we can use the waitForSelector function to wait for a specific element to be rendered on the page. We can also use the sleep function to simply pause the test for a specific amount of time.

12. How can we get elements that match multiple CSS selectors in Puppeteer?

We can use the document.querySelectorAll() method to get elements that match multiple CSS selectors in Puppeteer.

13. What is the usage of the evaluate() function in Puppeteer?

The evaluate() function in Puppeteer allows you to execute arbitrary JavaScript code inside of a page. This can be useful for extracting data from the page, or for interacting with the page in a way that is not possible with the standard Puppeteer API.

14. How does Puppeteer help us automate performance testing for web apps?

Puppeteer can help us automate performance testing for web apps by simulating user interactions and measuring the resulting performance metrics. This can help us identify potential bottlenecks and optimize our web apps for better performance.

15. What are some best practices when writing automated tests using Puppeteer?

Some best practices when writing automated tests using Puppeteer include:

-Using Page.evaluate() to execute scripts in the context of the page
-Using Page.waitFor() to wait for specific events to occur
-Using Page.click() to simulate user clicks
-Using Page.type() to simulate user input

16. Can you give me some examples of real-world websites that have been tested using Puppeteer?

Yes, some real-world examples of websites that have been tested using Puppeteer include Google, Facebook, and Instagram.

17. What are some alternatives to Puppeteer if you need to run cross-browser tests?

There are a few alternatives to Puppeteer if you need to run cross-browser tests. One option is to use a headless browser, which is a browser that can run without a graphical user interface. Another option is to use a cloud-based testing service, which can provide you with access to a variety of different browsers.

18. What are some common situations where Puppeteer may not work as expected?

Some common situations where Puppeteer may not work as expected include if the target website is built with React or Angular, if the website uses a lot of AJAX or iframes, or if the website is heavily dynamic.

19. What is the difference between screenshotting and capturing PDFs in Puppeteer?

When you take a screenshot in Puppeteer, you are simply capturing a image of what is currently displayed on the page. This is useful if you want to save a static image of the page for later use. Capturing a PDF of the page will create a PDF document that includes all of the content on the page, including any dynamic content that may not be visible when the screenshot is taken. This is useful if you want to create a document that can be printed or shared electronically.

20. Is it possible to take screenshots of pages that require login authentication before they load? If yes, then how?

Yes, it is possible to take screenshots of pages that require login authentication before they load. You would need to use a tool like Puppeteer to automate the login process and then take the screenshot.