js获取前后n天的时间

function getDay(day){  
       var today = new Date();  
         
       var targetday_milliseconds=today.getTime() + 1000*60*60*24*day;          
  
       today.setTime(targetday_milliseconds); 
         
       var tYear = today.getFullYear();  
       var tMonth = today.getMonth();  
       var tDate = today.getDate();  
       tMonth = doHandleMonth(tMonth + 1);  
       tDate = doHandleMonth(tDate);  
       return tYear+"-"+tMonth+"-"+tDate;  
}  
function doHandleMonth(month){  
       var m = month;  
       if(month.toString().length == 1){  
          m = "0" + month;  
       }  
       return m;  
}  
    $("#today").text(getDay(0));
    $("#tomorrow").text(getDay(1));
    $("#houtian").text(getDay(2));

 
 
console.log("半年前："+getDay(-180));
console.log("三月前："+getDay(-90));
console.log("一月前："+getDay(-30));
console.log("昨天："+getDay(-1));
console.log("今天："+getDay(0));
console.log("明天："+getDay(1));
console.log("后天："+getDay(2));
console.log("一月后："+getDay(30));
console.log("三月后："+getDay(90));
console.log("半年后："+getDay(180));