whole_func_string: function getDatetimeUnit(min, max) {
    const diff = max.diff(min, 'days');
    let unit = 'month';
    if (diff <= 14) {
      unit = 'day';
    } else if (diff > 14 && diff <= 183) {
      unit = 'week';
    }
    return unit;
  }
func_code_string: function getDatetimeUnit(min, max) {
    const diff = max.diff(min, 'days');
    let unit = 'month';
    if (diff <= 14) {
      unit = 'day';
    } else if (diff > 14 && diff <= 183) {
      unit = 'week';
    }
    return unit;
  }
func_documentation_string: getDatetimeUnit - determine the unit of time for padding the axis
  
  @param {object} min, the min moment datetime object
  @param {object} max, the max moment datetime object
  @return {string} the datetime unit {day, week, month}