HeDate.js
function(month, year1, year2) {
    var leap1 = isLeap(year1 - 1);
    var leap2 = isLeap(year2 - 1);

    if(month < 5 + leap1) return 0;
    return leap2 - leap1;
  }
function(month, year1, year2) {
    var leap1 = isLeap(year1 - 1);
    var leap2 = isLeap(year2 - 1);

    if(month < 5 + leap1) return 0;
    return leap2 - leap1;
  }
function ( month , year1 , year2 ) { var leap1 = isLeap ( year1 - 1 ) ; var leap2 = isLeap ( year2 - 1 ) ; if ( month < 5 + leap1 ) return 0 ; return leap2 - leap1 ; }
returns 0, 1 or -1
returns 0 1 or - 1