js如何获取前后连续n天的时间

function GetDateStr(AddDayCount) { 
   var dd = new Date();
   dd.setDate(dd.getDate()+AddDayCount);//获取AddDayCount天后的日期
   var y = dd.getFullYear(); 
   var m = (dd.getMonth()+1)<10?"0"+(dd.getMonth()+1):(dd.getMonth()+1);//获取当前月份的日期，不足10补0
   var d = dd.getDate()<10?"0"+dd.getDate():dd.getDate();//获取当前几号，不足10补0
   return y+"-"+m+"-"+d; 
}
 
 
console.log("半年前："+GetDateStr(-180));
console.log("三月前："+GetDateStr(-90));
console.log("一月前："+GetDateStr(-30));
console.log("昨天："+GetDateStr(-1));
console.log("今天："+GetDateStr(0));
console.log("明天："+GetDateStr(1));
console.log("后天："+GetDateStr(2));
console.log("一月后："+GetDateStr(30));
console.log("三月后："+GetDateStr(90));
console.log("半年后："+GetDateStr(180));