What is a Headless Browser and What is it Used For?

Understanding What a Headless Browser Is

The "headless" element of "headless browsers" refers to the fact that they lack a key component – a graphical user interface (GUI). This means that the browser itself functions normally (accesses target websites, loads/unloads documents, presents information, etc.), but all these sequential actions happen in the backend without any graphical display for the user (e.g., icons, images, or search bar elements). Instead, software testing engineers prefer to use "Command Line" interfaces that process commands as text strings. 

What is a Headless Browser Used For? Explanations and Examples

First: Data Collection

Searching and extracting data with a headless browser is much more efficient because, for example, there is no need to load graphical elements, simplifying the data collection process. 

Headless browsers can be a useful tool when you need to run JavaScript (JS) or if you are not interested in writing complex query chains yourself. 

The only downside is that launching a browser takes more time and uses more random-access memory (RAM) compared to a user script. 

However, if the automation of data collection services is implemented based on a headless browser, it simplifies the process. Data collection automation tools help increase the success rate of visits to target websites, manage user agent rotation, and eliminate the need to collect cookie databases.  

Second: Test Automation 
Headless browsers are used to automate software development/operations tasks as well as quality assurance (QA). For example, tasks such as verifying the correct operation of submission forms are automated. 

Third: Performance Monitoring
Headless browsers use fast response times to test non-user interface aspects of a site (i.e., they use command lines to monitor backend performance). This avoids unnecessary "time/resource losses," such as manually refreshing a page. 

Fourth: Layout Analysis 
To ensure that all visual layouts appear as intended, developers and designers use headless browsers as an automation tool:

• layout screenshot capture 
• HTML/CSS rendering/interpretation 
• element color selection testing 
• JavaScript/AJAX testing 

Explanation of Headless Testing 

Headless testing is a technique that allows browser validation without considering the user interface or graphical user interface. It enables software quality assurance professionals to shorten the development cycle by providing developers with faster feedback. 

Advantages and Disadvantages of Headless Browsers 

Advantages of Headless Browsers 

• Headless browsers are faster than regular browsers – they load CSS and JavaScript much more quickly and do not need to open and render HTML. 
• Headless browsers are much more efficient at extracting specific data from target sites, such as competitor product prices.
• Headless browsers save developers time; for example, when performing unit testing of code changes (mobile and desktop), it can be done via the command line. 

Disadvantages of Headless Browsers 

• Headless browsers increase speed, but sometimes there is a trade-off, such as more difficult problem debugging. 
• The actions of a headless browser are limited to backend tasks, meaning it cannot help with frontend issues (e.g., taking GUI screenshots). 

Most Popular Headless Browsers

Below are the four most popular headless browsers today: 

#1: Google Puppeteer 
Puppeteer is essentially a Node library. It provides users with a very good application programming interface (API) for working with things like Chrome and the DevTools Protocol. 

#2: PhantomJS
A JavaScript API that comes with a headless WebKit that can be fully parsed. Supports JSON/DOM/SVG. 

#3: HtmlUnit
This is a zero-GUI browser specifically for Java programs. It includes an API that helps interact with pages, such as clicking links, filling forms, etc., using command lines rather than visual display. 

#4: Splinter
This open-source option is commonly used for testing Python-based web applications. You can put web interaction on autopilot, such as interacting with specific buttons/forms/URLs.

Summary 

Headless browsers are a very useful tool, especially when you need more efficient data collection, test automation, performance monitoring, and layout verification. Supplementing a "headless" browser with the right data collection infrastructure is crucial for browser automation. This includes making the crawler appear as a real user to avoid being blocked by target sites, as well as gaining access to the full request history with relevant debugging information for troubleshooting.