如何从数组中随机分配类

Question

我试图从jQuery中预设的列表中随机添加一个类到一个元素，例如

可用课程：Theme1，Theme2，Theme3

var NumClasses = 3
function randOrd() {
    return (Math.round(Math.random())-0.NumClasses); 
}
$(document).ready(function() {
    var klasses = [ 'Theme1', 'Theme2', 'Theme3' ];
    klasses.sort( randOrd );
    $("#main-body-header").addClass(klasses[i]);
});