Here a simple example, similar to your needs…
$w.onReady(async function () {
console.log("DisplayResolution: ", await getScreenSize())
});
function getScreenSize() {
let windowHeight
let windowWidth
let DisplayResolution
return wixWindow.getBoundingRect()
.then((windowSizeInfo) => {
windowHeight = windowSizeInfo.window.height;
windowWidth = windowSizeInfo.window.width;
DisplayResolution = windowWidth+"x"+windowHeight
// let x = windowWidth;
// let y = windowHeight
return (DisplayResolution)
});
}