dayjs/esm/plugin/isoWeek/index.js

import { D, W, Y } from '../../constant';
var isoWeekPrettyUnit = 'isoweek';
export default (function (o, c, d) {
  var getYearFirstThursday = function getYearFirstThursday(year, isUtc) {
    var yearFirstDay = (isUtc ? d.utc : d)().year(year).startOf(Y);
    var addDiffDays = 4 - yearFirstDay.isoWeekday();

    if (yearFirstDay.isoWeekday() > 4) {
      addDiffDays += 7;
    }

    return yearFirstDay.add(addDiffDays, D);
  };

  var getCurrentWeekThursday = function getCurrentWeekThursday(ins) {
    return ins.add(4 - ins.isoWeekday(), D);
  };

  var proto = c.prototype;

  proto.isoWeekYear = function () {
    var nowWeekThursday = getCurrentWeekThursday(this);
    return nowWeekThursday.year();
  };

  proto.isoWeek = function (week) {
    if (!this.$utils().u(week)) {
      return this.add((week - this.isoWeek()) * 7, D);
    }

    var nowWeekThursday = getCurrentWeekThursday(this);
    var diffWeekThursday = getYearFirstThursday(this.isoWeekYear(), this.$u);
    return nowWeekThursday.diff(diffWeekThursday, W) + 1;
  };

  proto.isoWeekday = function (week) {
    if (!this.$utils().u(week)) {
      return this.day(this.day() % 7 ? week : week - 7);
    }

    return this.day() || 7;
  };

  var oldStartOf = proto.startOf;

  proto.startOf = function (units, startOf) {
    var utils = this.$utils();
    var isStartOf = !utils.u(startOf) ? startOf : true;
    var unit = utils.p(units);

    if (unit === isoWeekPrettyUnit) {
      return isStartOf ? this.date(this.date() - (this.isoWeekday() - 1)).startOf('day') : this.date(this.date() - 1 - (this.isoWeekday() - 1) + 7).endOf('day');
    }

    return oldStartOf.bind(this)(units, startOf);
  };
});