js判断生效时间不得大于失效时间

<script type="text/javascript">

function check(){

//开始时间比结束时间大的验证

   var validtime = document.form1.validtime.value;
   var invalidtime = document.form1.invalidtime.value;
   var beginTimes=validtime.substring(0,10).split('-');
   var endTimes=invalidtime.substring(0,10).split('-');
   validtime=beginTimes[1]+'/'+beginTimes[2]+'/'+beginTimes[0]+'/'+ validtime.substring(10,19);
   invalidtime=endTimes[1]+'/'+endTimes[2]+'/'+endTimes[0]+'/'+invalidtime.substring(10,19);
   var a =(Date.parse(invalidtime)-Date.parse(validtime))/3600/1000;
   if(a<0){
   alert("失效时间不能小于生效时间!");
   return;
}
   var emergency = document.form1.emergency.value;
   if(emergency==""||regnull.test(emergency)){
       alert("请输紧急程度!");
       document.form1.emergency.focus();
       return;
   }

document.form1.submit();

}