<script language="javascript" type="text/javascript">
function now(){
    var today = new Date();
    var year=today.getYear();
    var month=today.getMonth()+1;
    var date=today.getDate();
    var hours=today.getHours();
    var minutes=today.getMinutes();
    var seconds=today.getSeconds();
    document.write(year+'-'+month+'-'+date+' '+hours+':'+minutes+':'+seconds)
}
now()
</script>

------解决方案--------------------
<input onblur="checkObjValue(this)">
<script language=javascript>
	function check(obj)
	{
		var str=obj.value
		var re=/^(\d{4})-(\d{2})-(\d{2})-(\d{2})-(\d{2})$/
		if(!re.test(str))
		return false;
		var strYear=RegExp.$1;
		var strMonth=RegExp.$2;
		strMonth=parseInt(strMonth,10)-1
		var strDate=RegExp.$3;
		strDate=parseInt(strDate,10)
		var strHour=RegExp.$4;
		strHour=parseInt(strHour,10)
		var strMinute=RegExp.$5;
		strMinute=parseInt(strMinute,10)
		var tempDate=new Date(strYear,strMonth,strDate,strHour,strMinute,0)
  		return (tempDate.getFullYear()==strYear)&&(tempDate.getMonth()==strMonth)&&(tempDate.getDate()==strDate)&&(tempDate.getHours()==strHour)&&(tempDate.getMinutes()==strMinute)
	}
	function checkObjValue(obj)
	{
		if(check(obj))
		{
			alert("正确")
		}else{
			alert("输入错误")
			obj.value=''
		}
	}
</script>