function datum() {

var now = new Date();
var tag = new Array ("So", "Mo", "Di", "Mi", "Do", "Fr", "Sa");
var monat = new Array ("01", "02", "03", "04", "05", "06", "07", "08", "09", "10", "11", "12");
var date = ((now.getDate()<10) ? "0" : "")+ now.getDate();

function vierstellig(number) {
        return (number < 1000) ? number + 1900 : number;
}

heute = tag[now.getDay()]+ " "  + date + "." + monat[now.getMonth()] + "." +(vierstellig(now.getYear()));

document.write("" + heute);
}