jsで日付好きな文字でjoinするのが見つからなかった

date.js

var date_string = function(d, join) {
  //Date -> 20150101
  var year = (d.getYear() + 1900).toString();
  var month = ('0' + (d.getMonth() + 1).toString()).slice(-2);
  var day = ('0' + d.getDate().toString()).slice(-2);
  return year + join + month + join + day;
}