Is it possible to calculate viewport or window width based on getBoundingClientRectAsync values of element which is in virtual DOM?

Running JS in web worker (amp-script):

let button = document.querySelector('.tooltip-trigger');

async function addTooltip(event) {

    tooltipElem = document.createElement('span'); 
    document.body.appendChild(tooltipElem);

    let coordsTrigger = await target.getBoundingClientRectAsync();

    // How to get right offset?
    let windowWidth = coordsTrigger.left + coordsTrigger.width;
    console.log(windowWidth);
    
}

Target Element (wrapped in amp-script):

<amp-script layout="fill" script="tooltip-async"><span class="tooltip-trigger"></span></amp-script>

The half working solution is to use window.innerWidth. Half working, because window.innerWidth value changes only after page reload, and is not changing on resize or any other event for some reason. Probably because it is running in amp-script web-worker DOM and not in main;

coordsTrigger out:

bottom: 383.65625
height: 24
left: 122.59375
right: 201.640625
top: 359.65625
width: 79.046875
x: 359.65625
y: 122.59375