js数组中如何随机取出一个值

 
<html> 
<boby> 
</body> 

<script language="javascript"> 
window.onload = function(){ 
var arr = ["太阳光大、父母恩大、君子量大、小人气大","成功是优点的发挥,失败是缺点的累积","不要小看自己,因为人有无限的可能", 
"口说好话、心想好意、身行好事","原谅别人就是善待自己","手心向下是助人,手心向上是求人;助人快乐,求人痛苦" 
]; 

var index = Math.floor((Math.random()*arr.length)); 
alert(arr[index]); 

} 
</script> 
</html>