'orientationchange' doesn't seem to be working in S1

Question

Recently started using S1. Developing a web app and trying to listen out for orientation change on iPad.

This works perfectly in full site mode on the iPad

function doOnOrientationChange() {
    switch(window.orientation) {  
        case -90:
        case 90:
        alert('landscape');
        break; 
        default:
        alert('portrait');
        break; 
    }
 }

window.addEventListener('orientationchange', doOnOrientationChange);

// Initial execution if needed
doOnOrientationChange(); 

But only once on initial page load in the S1 app.

Anyone have any suggestions or advice?