function randomInt(n){
    var iValue = Math.random() * n;
    var rNumber = Math.ceil(iValue)-1;
    if(rNumber==-1) rNumber++;
    return rNumber;
}
function displayImageRandom(){
    var _toPath = function(name) {
        return '/ja/header_img/' + name;
    }
    var h = $('headerimage');
    if (!h) return;

    var classes = h.className.split(' ');
    if ((classes.length > 1) && (classes[0] == 'random')) {
        h.src = map(_toPath, classes.slice(1))[randomInt(classes.length-1)];
    }
}
addLoadEvent(displayImageRandom);