Benchmark Overview

The provided benchmark, window.getComputedStyle vs. className vs. classList 2, measures the performance of three different approaches to check if an element has a specific CSS class: window.getComputedStyle, className, and classList. The test is designed to simulate a scenario where an application needs to frequently check if an element's display style is set to "none", which can be achieved by checking for the presence of the "hide" class.

Approaches Compared

1. window.getComputedStyle: This method retrieves the computed style of an element, and then checks if the display property has a value of "none" using the indexOf method.
2. className: This method returns all classes currently applied to an element as a single string, separated by spaces. The test checks if the "hide" class is present in this string using the includes method.
3. classList: This method provides a more modern alternative to className, returning an array-like object of classes applied to an element. The test uses the contains method to check if the "hide" class is present.

Pros and Cons

• window.getComputedStyle:
  • Pros: Can provide more fine-grained control over style checks, as it returns a specific property value (display). However, this approach requires parsing the computed style string, which can be slower.
  • Cons: Requires accessing the getComputedStyle method, which may have additional overhead due to its asynchronous nature and potential DOM traversal costs.
• className:
  • Pros: Simple and straightforward implementation, with minimal overhead. However, this approach returns all classes as a single string, which can lead to slower performance if many classes are present.
  • Cons: May be slower due to the need to concatenate class strings, which can be expensive.
• classList:
  • Pros: Provides a more modern and efficient alternative to className, with better performance characteristics. It returns an array-like object of classes, allowing for faster membership checks using the contains method.
  • Cons: May require support for newer browsers or polyfills if not already included.

Library and Special JS Feature

The test uses the classList property, which is a modern JavaScript feature introduced in ECMAScript 2015 (ES6). This property provides an array-like interface to access and manipulate class names of elements. While this approach offers better performance, it may require additional support or polyfills for older browsers.

Other Considerations

• Browser Support: The test is designed to run on Chrome 113 on Linux desktop platforms. Other browsers and operating systems may exhibit different performance characteristics.
• DOM Traversal Costs: The getComputedStyle method involves accessing the DOM, which can incur additional overhead due to tree traversal costs.

Alternatives

If you need to compare other approaches or consider alternative solutions, here are a few options:

• CSSOM: Instead of using window.getComputedStyle, you could use the CSS Object Model (CSSOM) API to access and manipulate styles directly. This would eliminate the need for parsing computed style strings.
• Native JavaScript Methods: You could explore native JavaScript methods like Element.matches() or Element.contains(), which provide more efficient membership checks compared to string-based approaches.

When choosing a solution, consider factors such as performance requirements, browser support, and code maintainability.