JavaScript ResizeObserver Polyfill

The ResizeObserver API is a powerful built-in browser feature that allows developers to asynchronously observe changes to the size of DOM elements. This is incredibly useful for responsive UIs, dynamic layouts, and performance optimizations. However, older browsers lack native support for ResizeObserver. This challenge asks you to implement a polyfill for ResizeObserver in JavaScript.

Problem Description

Your task is to create a JavaScript ResizeObserver polyfill that mimics the behavior of the native ResizeObserver API as closely as possible. This polyfill should work in environments where ResizeObserver is not natively available.

Key Requirements:

1. Constructor:

   • The polyfill should be exposed as a constructor function named ResizeObserver.
   • It must accept a single argument: a callback function. This callback will be invoked whenever an observed element's size changes.
   • The callback function receives an array of ResizeObserverEntry objects and the observer instance itself as arguments.

2. observe(target, options) Method:

   • This method should attach the observer to a specified target DOM element.
   • The options object is optional and can contain box property ('content-box' or 'border-box'). If not provided, it defaults to 'content-box'.
   • The polyfill should start monitoring the target element for size changes.

3. unobserve(target) Method:

   • This method should detach the observer from a specific target DOM element, stopping further observation for that element.

4. disconnect() Method:

   • This method should detach the observer from all observed elements.

5. ResizeObserverEntry Object:

   • When the callback is invoked, it should receive an array of ResizeObserverEntry objects. Each entry must have the following properties:
     • target: The DOM element whose size changed.
     • contentRect: A DOMRectReadOnly object representing the element's content area's size and position.
     • contentBoxSize: An array containing a single ResizeObserverSize object with inlineSize and blockSize properties, representing the dimensions of the content box. (If box option is 'content-box').
     • contentBoxSize: An array containing a single ResizeObserverSize object with inlineSize and blockSize properties, representing the dimensions of the content box. (If box option is 'content-box').
     • contentBoxSize: An array containing a single ResizeObserverSize object with inlineSize and blockSize properties, representing the dimensions of the content box. (If box option is 'content-box').
     • contentBoxSize: An array containing a single ResizeObserverSize object with inlineSize and blockSize properties, representing the dimensions of the content box. (If box option is 'content-box').
     • contentBoxSize: An array containing a single ResizeObserverSize object with inlineSize and blockSize properties, representing the dimensions of the content box. (If box option is 'content-box').
     • contentBoxSize: An array containing a single ResizeObserverSize object with inlineSize and blockSize properties, representing the dimensions of the content box. (If box option is 'content-box').
     • contentBoxSize: An array containing a single ResizeObserverSize object with inlineSize and blockSize properties, representing the dimensions of the content box. (If box option is 'content-box').
     • contentBoxSize: An array containing a single object with and properties, representing the dimensions of the content box. (If option is .