js判断当前时间前几天和格式校验

function time(addday)
{							
	var now= new Date();				
	nowdate=now.getDate();
	//alert(nowdate);
	now.setDate(nowdate+addday);//获取addday天后的日期 
	year=now.getFullYear();
	month=now.getMonth();
	date=now.getDate();
	return now;
}	

<script>
	function getBeforeDate(n){
		var n = n;
		var d = new Date();
		var year = d.getFullYear();
		var mon=d.getMonth()+1;
		var day=d.getDate();
		if(day <= n){
			if(mon>1) {
			        mon=mon-1;
			 }
			else {
			     year = year-1;
			     mon = 12;
			  }
		}
		d.setDate(d.getDate()-n);
		 year = d.getFullYear();
		mon=d.getMonth()+1;
		day=d.getDate();
		s = year+"-"+(mon<10?('0'+mon):mon)+"-"+(day<10?('0'+day):day);
		return s;
	}
</script>

$("#go").click(function(){
	//alert(getBeforeDate(341));
	var projectname="<%=session.getAttribute("projectname_session")%>";					
	var modelname= document.getElementById("codeid").value;
	var d=document.getElementById("enddate").value;
	var year= d.substring(0,4);
	var mon=d.substring(5,d.lastIndexOf("-"));
	var day=d.substring(d.lastIndexOf("-")+1,d.length);
	var selectDate = year+"-"+((mon.length==1)?('0'+mon):mon)+"-"+(day.length==1?('0'+day):day);
	 alert(selectDate);
	//alert(selectDate);
	if(selectDate<=getBeforeDate(341)||(selectDate>=getBeforeDate(-1))){
		var info="No Data!
Please Select a Valid Date: ""+getBeforeDate(341)+" ~ "+getBeforeDate(0)+""";
		alert(info);
	}
	else{
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