javascript的有效校验

        //年月日期有效性检验
  	function yearAndMonthCheck()
  	{
  		var  flag = true;
  		var currentyear = new Date().getFullYear();
  		var currentmonth = new Date().getMonth();
  		var yearvalue =  $("#fsyear").val();
  		var monthvalue = $("#fsmonth").val();
  		if(yearvalue.length<4)
  		{
  			alert("所输入年限不能小于4位数字");
  			flag = false;
  		}
  		if((yearvalue !=null && yearvalue!="") || (monthvalue != null && monthvalue !=""))
  		{
  			var stepyear = parseInt(yearvalue) - currentyear;
  			var stepmonth = parseInt(currentmonth) - monthvalue;
  			if(stepyear > 0)
  			{
  				alert("输入年限不能大于本年");
  				flag = false;
  			}
  			if(stepmonth >12)
  			{
  				alert("月份不能大于12");
  				flag = false;
  			}
  			//if(stepmonth > 0)
  			//{
  			//	alert("输入年限不能大于本月");
  			//	flag = false;
  			//}
  		}
  		return flag;
  	}