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>