orientatie.js

var orientation;

// niet alle mobiele browsers ondersteunen de 'orientationchange' dus we gebruiken 'resize' als fallback
var supportsOrientationChange = "onorientationchange" in window,
    orientationEvent = supportsOrientationChange ? "orientationchange" : "resize";

window.addEventListener(orientationEvent, setOrientation, false);
window.addEventListener("load", setOrientation, false);

function setOrientation(){
    orientation = (screen.width > screen.height) ? "landscape" : "portret";
    
    // hieronder doen wat je wilt afhangend van de orientatie
    if(orientation == "portret"){
        // 2 elementen onder elkaar;
        document.getElementById('element_1').style.cssFloat = "none";
        document.getElementById('element_2').style.cssFloat = "none";
    } else {
        // 2 elementen naast elkaar;
        document.getElementById('element_1').style.cssFloat = "left";
        document.getElementById('element_2').style.cssFloat = "left";
    }
}