js判断生效时间不得大于失效时间的思路及代码

<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();
}
<script>