window.addEventListener('orientationchange', setOrientation, false);
function setOrientation() {
var orient = Math.abs(window.orientation) === 90 ? 'landscape' : 'portrait';
if (orient == "portrait") {
window.alert("This app is only available in landscape mode, please switch back");
$("html").css("display", "none");
} else {
$("html").css("display", "block");
}
}