Abwechelnde Bilder im Header

var images = [
    '/img/eins.png',
    '/img/zwei.png',
    '/img/drei.png',
    '/img/vier.png',
];

window.onload = function () {
    var image = images[Math.floor(Math.random() * images.length)];
    document.getElementById('header').style.background = 'url(' + image + ')';
};