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

Benchmark Definition:

The website measures the performance of two methods: contains() and closest(). The contains() method checks if an element is contained within another element, while closest() finds the closest ancestor element that matches a specified selector.

Script Preparation Code:

var box = document.getElementById('div1');
var clicked = document.getElementById('div3');

This code retrieves two elements from the HTML page using their IDs: box (the outermost container) and clicked (a child element within box).

Html Preparation Code:

<div id='div1'>
  <div id='div2'>
    <div id='div3'>
    </div>
  </div>
</div>

This HTML code defines the structure of the page, where div1 is the outermost container, and div3 is a child element within it.

Individual Test Cases:

There are two test cases:

contains

const isClickInside = box.contains(clicked);
return isClickInside;

This code checks if clicked (the innermost element) is contained within box (the outermost container). The contains() method returns a boolean value indicating whether the element is found.

closest

const isClickInside = clicked.closest('#div1');
return isClickInside;

This code uses the closest() method to find the closest ancestor element that matches the selector #div1. Since div3 is already inside div1, this method will return a reference to itself. The result is then returned.

Pros and Cons:

• contains():
  • Pros:
    • Simple and intuitive
    • Works well for most cases
  • Cons:
    • Can be slower than closest() due to the overhead of checking each element in the DOM tree
• closest():
  • Pros:
    • Often faster than contains()
    • Handles cases where the target element is not directly contained within another element
  • Cons:
    • More complex and may have a higher chance of errors

Library:

The closest() method uses the Web Content Accessibility Guidelines (WCAG) 2.1 specification, which defines an API for finding the closest ancestor element that matches a specified selector.

Special JS Feature/Syntax:

None mentioned in this benchmark definition.

Other Alternatives:

If you need to check if an element is contained within another, you can use:

• contains() with the Element.contains() method (Chrome 114)
• closest() with a more specific selector (e.g., closest('#div1'))

Keep in mind that the performance difference between these methods may vary depending on your specific use case and the browser being used.