js 验证时间先后

function comptime(beginTime,endTime){
    alert(beginTime);
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);

var a =(Date.parse(endTime)-Date.parse(beginTime))/3600/1000;

if(a<0){
return false;
}
return true;
}