用js来验证日期的格式正确与否

  function CheckDate(registeredTime){       
     var reg=/^(\d{4})(\d{2})(\d{2})$/;   
        if(!reg.test(registeredTime)){   
            alert("日期格式不正确!\n正确格式为:20040101");   
            return false;   
            }   
          
            var year=registeredTime.substring(0,4);   
            var month=registeredTime.substring(4,6);   
            var date=registeredTime.substring(6,8);    
            if(!checkYear(year)){return false;}   
            if(!checkMonth(month)){return false;}   
            if(!checkDate(year,month,date)){return false;}   
            return true;   
        }   
    function checkYear(year){   
        if(isNaN(parseInt(year))){   
            alert("年份输入有误,请重新输入!");   
             return false;   
        }   
        else if(parseInt(year)<1950 || parseInt(year) >2050)   
        {    
            alert("年份应该在1950-2050之间!");    
            return false;   
        }   
        else return true;   
        }   
    function checkMonth(month){   
        if(isNaN(parseInt(month,10))){alert("月份输入有误,请重新输入!"); return false;}