js 取年月日与年月日加减

 <script language="javascript">  
    //取值
    var myDate = new Date();  
    myDate.getYear();       //获取当前年份(2位)  
    myDate.getFullYear();   //获取完整的年份(4位,1970-????)  
    myDate.getMonth();      //获取当前月份(0-11,0代表1月)  
    myDate.getDate();       //获取当前日(1-31)  
    myDate.getDay();        //获取当前星期X(0-6,0代表星期天)  
    myDate.getTime();       //获取当前时间(从1970.1.1开始的毫秒数)  
    myDate.getHours();      //获取当前小时数(0-23)  
    myDate.getMinutes();    //获取当前分钟数(0-59)  
    myDate.getSeconds();    //获取当前秒数(0-59)  
    myDate.getMilliseconds();   //获取当前毫秒数(0-999)  
    myDate.toLocaleDateString();    //获取当前日期  
    var mytime=myDate.toLocaleTimeString();    //获取当前时间  
    myDate.toLocaleString( );       //获取日期与时间  
if (mytime<"23:30:00")  
{  
alert(mytime);  
}  

 <script language="javascript">  
    //日期加减
   function addDate(date,days){
    var d=new Date(date);
    d.setDate(d.getDate()+days);
    var m=d.getMonth()+1;
    return d.getFullYear()+'-'+m+'-'+d.getDate();
  }

   var dd="2014-02-28".split("-");
   var today = new Date(dd[0],dd[1]-1,dd[2]);
   document.write(addDate(today,1));

 <script language="javascript">  
    //日期加减
    Date.prototype.Format = function(fmt){
    //author: meizz 
    var o =
     { 
        "M+" : this.getMonth() + 1, //月份 
        "d+" : this.getDate(), //日 
        "h+" : this.getHours(), //小时 
        "m+" : this.getMinutes(), //分 
        "s+" : this.getSeconds(), //秒 
        "q+" : Math.floor((this.getMonth() + 3) / 3), //季度 
        "S" : this.getMilliseconds() //毫秒 
     }; 
    if (/(y+)/.test(fmt)) 
         fmt = fmt.replace(RegExp.$1, (this.getFullYear() + "").substr(4 - RegExp.$1.length)); 
    for (var k in o) 
        if (new RegExp("(" + k + ")").test(fmt)) 
             fmt = fmt.replace(RegExp.$1, (RegExp.$1.length == 1) ? (o[k]) : (("00" + o[k]).substr(("" + o[k]).length))); 
    return fmt; 
}

Date.prototype.addDays = function(d){
    this.setDate(this.getDate() + d);
};

Date.prototype.addWeeks = function(w){
    this.addDays(w * 7);
};

Date.prototype.addMonths= function(m){
    var d = this.getDate();
    this.setMonth(this.getMonth() + m);

    if (this.getDate() < d)
        this.setDate(0);
};


Date.prototype.addYears = function(y){
    var m = this.getMonth();
    this.setFullYear(this.getFullYear() + y);

    if (m < this.getMonth()) 
     {
        this.setDate(0);
     }
};

var dd="2014-4-04".split("-");
var today = new Date(dd[0],dd[1]-1,dd[2]);

today.addDays(27);//加减日期操作
//document.write(today.getFullYear()+"-"+today.getMonth()+"-"+today.getDate());
document.write(today.Format("yyyy-MM-dd"));