weekyear.js

export default (o, c) => {
  const proto = c.prototype;
  proto.weekYear = function () {
    const month = this.month();
    const weekOfYear = this.week();
    const year = this.year();
    if (weekOfYear === 1 && month === 11) {
      return year + 1;
    }
    if (month === 0 && weekOfYear >= 52) {
      return year - 1;
    }
    return year;
  };
};