Let's break down the provided benchmark definition and test cases to understand what's being tested.

Benchmark Definition

The website provides a JSON object representing the benchmark, which includes:

• Name: The name of the benchmark, "computedStyleMap vs getComputedStyle".
• Description: A brief description of the benchmark, but it's empty in this case.
• Script Preparation Code and Html Preparation Code: These are empty, suggesting that the benchmark doesn't require any specific script or HTML setup.

Test Cases

The benchmark has two individual test cases:

1. getComputedStyle
   • The benchmark definition is a JavaScript code snippet that:
     • Selects an HTML element (<div class="foo">) using document.querySelector.
     • Enters a loop with 15,000 iterations (using var i = 15000;).
     • Inside the loop, it uses window.getComputedStyle(el) to get the computed style of the selected element and retrieves the value of the 'color' property.
2. computedStyleMap
   • The benchmark definition is a JavaScript code snippet that:
     • Selects an HTML element (<div class="foo">) using document.querySelector.
     • Enters a loop with 15,000 iterations (using var i = 15000;).
     • Inside the loop, it uses el.computedStyleMap().get('color') to retrieve the value of the 'color' property from the computed style map.

What's being tested

The benchmark is testing two approaches:

1. getComputedStyle: This approach uses the built-in window.getComputedStyle() function to get the computed style of an element.
2. computedStyleMap: This approach uses the el.computedStyleMap() method, which is not a standard property of HTML elements. The implementation of this method is specific to each browser.

Pros and Cons

1. getComputedStyle
   • Pros:
     • Widely supported by most browsers.
     • Efficient, as it only retrieves the relevant style properties.
   • Cons:
     • May incur additional overhead due to the function call.
2. computedStyleMap
   • Pros:
     • May be faster than getComputedStyle due to reduced overhead.
   • Cons:
     • Limited browser support (specific implementation may vary).
     • May not work in older browsers.

Library/Implementation

The el.computedStyleMap() method is likely an implementation-specific feature, possibly part of the Web API or a custom library. The specific library or implementation used by the benchmark is not specified in the provided information.

Special JS feature/Syntax

There is no mention of any special JavaScript features or syntax in the benchmark definition.

Alternatives

Other alternatives to compare include:

• CSSOM: This approach uses the CSSOM (Cascading Style Sheets Object Model) API, which provides a more efficient way to manipulate styles.
• CSS-OM: This is a similar alternative, using the CSS Object Model.
• DOM manipulation: This approach would involve manually updating the element's style properties, which may be slower and less efficient than using getComputedStyle or computedStyleMap.

Keep in mind that this analysis assumes that the provided benchmark definition and test cases are accurate representations of the actual code being tested.