This benchmark compares two methods for retrieving the computed styles of an HTML element in the browser: getComputedStyle and computedStyleMap. The goal is to evaluate their performance and to understand the pros and cons of each approach.

Benchmark Overview

The benchmark runs two tests:

1. getComputedStyle: A traditional method to obtain the computed style of an element. The test executes this method in a loop to measure how many times it can retrieve the color property of an element with the class .foo.

2. computedStyleMap: A newer method that returns a CSSStyleValueMap representing all computed CSS properties in a structured format. This also retrieves the color property but does so in a way that allows developers to access more detailed information about individual style properties.

Performance Results

The benchmark results indicate the performance of each method in terms of executions per second:

• computedStyleMap: 12,807,623 executions per second
• getComputedStyle: 1,633,346.125 executions per second

The numbers reveal that computedStyleMap is significantly faster than getComputedStyle in this specific test.

Pros and Cons of Each Method

getComputedStyle

• Pros:

  • Widely supported across all modern browsers and has a long-standing presence in web development.
  • Straightforward to use for retrieving a specific CSS property value.

• Cons:

  • Performance is comparatively lower, especially in cases where frequent style calculations are needed.
  • Returns a string value for style properties, which may require parsing for complex types or calculations.

computedStyleMap

• Pros:

  • Offers better performance as seen in the benchmark results.
  • Provides a structured representation of CSS properties, allowing easier manipulation and access to specific attributes or values.
  • Supports new CSS value types directly, enhancing the ability to work with different types of CSS properties.

• Cons:

  • May not be as familiar to developers who are used to getComputedStyle, requiring some ramp-up time to fully understand and adopt.
  • Since it's newer, there may be limited support in older browsers or edge cases where fallback methods are necessary.

Considerations

When using either approach, consider the browser compatibility requirements for your project. While most modern browsers support computedStyleMap, some older versions or niche browsers may only support getComputedStyle. Additionally, while the performance advantage of computedStyleMap is notable, profiling the actual performance improvements in the context of your specific application and use case is advised.

Alternatives

In addition to these methods, other alternatives for manipulating or reading computed styles could include:

• CSS Variables: If a project is heavily reliant on dynamic styles, using CSS custom properties could be an alternative way to manage styles efficiently with JavaScript or CSS.
• Element.style: If styles are applied inline, accessing elements through the style property can provide immediate access to applied styles without needing to use either method.
• CSS-in-JS Libraries: Libraries like Styled Components or Emotion in React enable the creation of styled components that dynamically handle styles based on props.

Overall, the choice between these methods ultimately depends on the performance requirements of your application and the specificities of the styles being manipulated.