javascript比较日期大小

function compareDate(DateOne,DateTwo)
{ 

var OneMonth = DateOne.substring(5,DateOne.lastIndexOf ("-"));
var OneDay = DateOne.substring(DateOne.length,DateOne.lastIndexOf ("-")+1);
var OneYear = DateOne.substring(0,DateOne.indexOf ("-"));

var TwoMonth = DateTwo.substring(5,DateTwo.lastIndexOf ("-"));
var TwoDay = DateTwo.substring(DateTwo.length,DateTwo.lastIndexOf ("-")+1);
var TwoYear = DateTwo.substring(0,DateTwo.indexOf ("-"));

if (Date.parse(OneMonth+"/"+OneDay+"/"+OneYear) >
Date.parse(TwoMonth+"/"+TwoDay+"/"+TwoYear))
{
return true;
}
else
{
return false;
}

}

举例：
alert(compareDate(''2008-12-01'',''2009-05-02'''));
目前知支持年－月－日这样的格式