js，昨天的日期

var mydate = new Date();
        var yester = mydate-24*60*60*1000;
        var yesterday = new Date();
        yesterday.setTime(yester);
                   var str = "" + yesterday.getFullYear() + "-";
                       if (yesterday.getMonth()>=9) {
                           str+=(yesterday.getMonth()+1) + "-";
                       } else{

                           str +="0"+(yesterday.getMonth()+1)+"-";
                       }
                      if ((yesterday.getDate())<10) {
                          str+="0"+(yesterday.getDate());
                      } else{
                          str += (yesterday.getDate());
                      }
                       $("#mydata").val(str);