what is headless browser
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Adelina Kiskyte

Oct 02, 2020 5 min read

In short, a headless browser is a web browser without a graphical user interface (GUI). GUI includes digital elements that users interact with, such as buttons, icons, and windows. But there is much more you need to know about a headless browser.

In this article, you will learn what a headless browser is, what it is used for, what is headless Chrome and what other browsers are most popular in headless mode. We will also discuss the primary limitations of headless browser testing.

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What is a headless browser?

Headless browser is a web browser that is not configured with a Graphical User Interface (GUI). It is mostly used by software test engineers, because browsers without a GUI perform faster since they do not have to draw visual content. One of the largest benefits of headless browsers is their ability to be run on servers without GUI support. 

Headless browsers are usually executed via command line, or via network communication.

Headless Chrome is one of the most popular headless browsers

What is a headless browser used for?

The most common use case for headless browsers is web page testing. Headless browsers easily understand HTML pages and interpret them as any other browser. They depict style elements, including colors, fonts, layouts, etc.

So, what is the use of headless browser testing?

  • Automation

Headless browsers are used for automation tests in order to check submission forms, mouse clicks, keyboard inputs, etc. Basically, it includes anything that can be automated to save time and effort in any part of the software delivery cycle, including development, quality assurance, and installation. Automated tests can also be run for JavaScript libraries.

  • Layout testing

Headless browsers can render and interpret HTML and CSS elements just like a real browser. They are used for layout checks, for example to determine the default page width and element coordinates. Headless browsers also allow color selection testing for various elements. JavaScript and AJAX execution can be tested as well. Developers often automate screen captures in headless browsers in order to test the layout.

  • Performance

Website performance can be quickly tested using a headless browser. Since a browser without GUI loads websites much faster, performance tasks that do not require UI interaction can be tested via command line. In such tasks, there is no need to manually refresh pages. While this saves time and effort, it is important to note that only small performance tasks such as log in tests can be examined with a headless browser.

  • Data extraction

When it comes to web scraping and data extraction with a headless browser, there is often no need to start a website. Web scraping with a headless browser allows quickly navigating websites and collecting public data.

One of the main requirements for headless browsers is to be able to run on low resources. The browser should run in the background without significantly slowing down other tasks being performed by the system. 

Different headless browsers perform better in different testing scenarios. For this reason, developers often have to test various options to find the best combination of tools for their case. Here are some of the most popular headless browsers and their main features:

  • Google Chrome can run in a headless environment and provide a regular browser context without using up as much memory. Google Chrome headless mode is available in version 59 or higher. The most common tasks performed in Headless Chrome include printing the Document Object Model (DOM), creating a PDF, and taking screenshots.
  • Mozilla Firefox in headless mode can be connected to different APIs. The most popular framework to use with Firefox is Selenium. Headless Firefox is mostly used for running automated tests as it makes the testing process more efficient. 
  • HtmlUnit is written in Java and used to automate different ways in which users interact with websites. This headless web browser is most popular for testing e-commerce websites as it is best for testing submission forms, website redirects, and HTTP authentication.

Phantom JS is also worth mentioning, because it used to be a popular headless web browser. Many developers have compared PhantomJS vs HtmlUnit. However, Phantom JS has been discontinued for a few years now. It was open source, supported by contributions from dedicated developers.

Limitations of headless browser testing

Headless browser testing has its limitations. Here are some examples:

  • Testing with headless browsers may shift developer’s attention towards fixing bugs that only appear when using browsers in a headless environment. However, it is important not to forget that users will hardly ever visit the website with a headless browser. So focusing on issues that appear on a regular browser should be a priority.
  • During headless browser testing, some pages load too fast, making it difficult to debug inconsistent failures on locating elements.

Conclusion

Headless browsers work much faster than regular browsers, since they do not have to load all the content that contributes to user experience. 

Due to their high speed, headless browsers are often used for web page testing. They are employed in testing various automation tasks on a website, its performance and layout. Data extraction is another common use case for headless browsers.

Some of the most popular web browsers, including Chrome and Mozilla Firefox come in headless mode.  

However, headless browsers also have limitations and in some cases testing should be performed in regular browsers. 

If you would like to learn more about web scraping and data gathering with a headless browser, check out our blog post Web Scraping With Selenium: DIY or Buy?

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About Adelina Kiskyte

Adelina Kiskyte is a Content Manager at Oxylabs. Adelina constantly follows tech news and loves trying out new apps, even the most useless. When she is not glued to her phone, she also enjoys reading self-motivation books and biographies of tech-inspired innovators. Who knows, maybe one day she will create a life-changing app of her own!

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