Let's break down the benchmark and explain what is being tested.

Benchmark Description

The benchmark measures the performance of three different approaches to retrieve the height of an HTML element:

1. getComputedStyle: Uses the getComputedStyle method to get the computed style attribute of the element.
2. getBoundingClientRect: Uses the getBoundingClientRect method to get the size of the bounding rectangle of the element.
3. clientHeight: Uses the clientHeight property to get the height of the element's content area.

Approaches Comparison

The three approaches are compared in terms of their performance, which is measured by the number of executions per second.

• getComputedStyle: This approach is considered slower because it:
  • Requires a single DOM query to retrieve the element.
  • Uses a CSSOM (CSS Object Model) API call to get the computed style attribute, which can be slow due to the complexity of CSS calculations.
  • Returns an object with various properties, including height, which may require additional processing.
• getBoundingClientRect: This approach is considered faster because it:
  • Is generally faster than getComputedStyle since it doesn't involve a CSSOM API call and returns only the height property.
  • Requires only one DOM query to retrieve the element.
• clientHeight: This approach is considered slower than getBoundingClientRect but potentially faster than getComputedStyle since it:
  • Returns only the height of the content area, which may be less computationally expensive.
  • May be optimized by the browser.

Library and Special JS Feature

There are no libraries used in this benchmark. However, note that getComputedStyle uses a proprietary API (CSSOM) that is not part of the standard JavaScript API.

Considerations

When choosing an approach, consider the following factors:

• Accuracy: If you need precise control over the element's style and layout, getComputedStyle might be a better choice.
• Performance: If speed is critical, getBoundingClientRect or clientHeight might be a better option.
• Code simplicity: clientHeight requires less code than getComputedStyle or getBoundingClientRect.

Alternatives

Other approaches to retrieve an element's height include:

• Using the offsetHeight property (not shown in this benchmark).
• Creating a custom function to calculate the height based on the element's size and layout.

Keep in mind that these alternatives might have different performance characteristics compared to the methods tested in this benchmark.