js 时间比较大小

var beginTime = "2009-09-21 00:00:00";
var endTime    = "2009-09-21 00:00:01";
var beginTimes = beginTime.substring(0,10).split('-');
var endTimes   =  endTime.substring(0,10).split('-');

beginTime = beginTimes[1]+'-'+beginTimes[2]+'-'+beginTimes[0]+' '+beginTime.substring(10,19);
endTime    = endTimes[1]+'-'+endTimes[2]+'-'+endTimes[0]+' '+endTime.substring(10,19);

alert(beginTime+"aaa"+endTime);
alert(Date.parse(endTime));
alert(Date.parse(beginTime));

var a =(Date.parse(endTime)-Date.parse(beginTime))/3600/1000;
if(a<0){
	alert("endTime小!");
}else if (a>0){
	alert("endTime大!");
}else if (a==0){
	alert("时间相等!");
}else{
           return 'exception'}
 }