อยากได้โค้ด javascript ที่ใช้บวกกับลบวันที่ ขอบคุณค่ะ

<script>
var d = new Date('2015-11-06');
var _1day = 24 * 60 * 60 * 1000; 
var nextDay = new Date( d.getTime() + _1day );
var prevDay = new Date( d.getTime() - _1day );
document.write( nextDay + '<br>');
document.write( prevDay + '<br>');
</script>

              var d = new Date(date);
              var _1day = 24 * 60 * 60 * 1000; 
              var prevDay = new Date( d.getTime() - _1day );

              var m = prevDay.getMonth();
              var d = prevDay.getDate();
              var y =  prevDay.getFullYear();
              if(m <= 1)
              {m = "0"+m;}
              if(d <= 9)
              {d = "0"+d;}
              m = m+1;
       
              var prev = y + "-" + m + "-" + d;