js如何获取前后连续n天的时间

 1 function GetDateStr(AddDayCount) { 
 2    var dd = new Date();
 3    dd.setDate(dd.getDate()+AddDayCount);//获取AddDayCount天后的日期
 4    var y = dd.getFullYear(); 
 5    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
 6    var d = dd.getDate()<10?"0"+dd.getDate():dd.getDate();//获取当前几号，不足10补0
 7    return y+"-"+m+"-"+d; 
 8 }
 9  
10  
11 console.log("半年前："+GetDateStr(-180));
12 console.log("三月前："+GetDateStr(-90));
13 console.log("一月前："+GetDateStr(-30));
14 console.log("昨天："+GetDateStr(-1));
15 console.log("今天："+GetDateStr(0));
16 console.log("明天："+GetDateStr(1));
17 console.log("后天："+GetDateStr(2));
18 console.log("一月后："+GetDateStr(30));
19 console.log("三月后："+GetDateStr(90));
20 console.log("半年后："+GetDateStr(180));