IntersectionObserver superseded by Proxy?

Question

It makes sense to me that IntersectionObserver is preferred to adding scroll-based event listeners these days. Great.

However, I read here and here that a Proxy offers a more desirable way to do this and that Object.observe is perhaps even obsolete.

After reading about Proxy traps for a while, I still can't get my head around how I would use them in my imaginary use case below - or find any good references for it.

The imaginary use case:

1. Generate an arbitrary number of divs with random background colours.
2. Each div gets an IntersectionObserver.
3. When isIntersecting == true for any of the divs, the body's background colour changes to that of the div.

How would I even begin to think about implementing this using proxies?

Fiddle here. It actually creates an attractive - if counterintuitive - effect.

let numberOfDivs = 5;

function createDiv(divNumber) {

    // set the div's tag name, class name and a unique ID
    let aDiv = document.createElement('div');
    aDiv.className = 'my-divs';
    aDiv.id = 'div' + divNumber;

    // set a random hex bg colour for the div;
    // drops a leading zero 1/16 of the time but it's not material to the example
    aDiv.style.backgroundColor = '#' + Math.floor(Math.random()*16777215).toString(16);

    // append the div to the body
    document.body.appendChild(aDiv);

    // set IntersectionObserver on the div
    let observer = new IntersectionObserver(whatsIn, {threshold: 0.5});
    observer.observe(aDiv);

}

// create the divs

for ( let i = 0; i < numberOfDivs; i++ ) {
    let newDiv = createDiv(i);
}

// examine the IntersectionObserver output whenever isIntersecting changes
function whatsIn(payload) {
    console.log("Is " + payload[0].target.id + " intersecting? " + payload[0].isIntersecting);

    // change background color based on most recent isIntersecting == true
    document.body.style.backgroundColor =
        payload[0].isIntersecting
            ? payload[0].target.style.backgroundColor
            : document.body.style.backgroundColor;
}