Find which shift you are on firefighting

function shift(){
  var oneDay = 24*60*60*1000; // hours*minutes*seconds*milliseconds
  var ashift = new Date(2015,08,15);
  var bshift = new Date(2015,08,16);
  var cshift = new Date(2015,08,17);
  var today = new Date();
  today.setHours(0,0,0,0);

  var ashift = Math.round(Math.abs((ashift.getTime() - today.getTime())/(oneDay)));
  var bshift = Math.round(Math.abs((bshift.getTime() - today.getTime())/(oneDay)));
  var cshift = Math.round(Math.abs((cshift.getTime() - today.getTime())/(oneDay)));
  //diffDays % 2;
  if(ashift % 3 === 0){
    return "A shift";
  }else if(bshift % 3 === 0){
    return "B shift";
  }else if(cshift % 3 === 0){
    return "C shift";
  }else{
    return "unkown shift";
  }

}