function startOf()

in charts/shared/moment.js [4088:4149]
59 lines of code
16 McCabe index (conditional complexity)

function startOf(units) {
    var time, startOfDate;
    units = normalizeUnits(units);
    if (units === undefined || units === 'millisecond' || !this.isValid()) {
        return this;
    }

    startOfDate = this._isUTC ? utcStartOfDate : localStartOfDate;

    switch (units) {
        case 'year':
            time = startOfDate(this.year(), 0, 1);
            break;
        case 'quarter':
            time = startOfDate(
                this.year(),
                this.month() - (this.month() % 3),
                1
            );
            break;
        case 'month':
            time = startOfDate(this.year(), this.month(), 1);
            break;
        case 'week':
            time = startOfDate(
                this.year(),
                this.month(),
                this.date() - this.weekday()
            );
            break;
        case 'isoWeek':
            time = startOfDate(
                this.year(),
                this.month(),
                this.date() - (this.isoWeekday() - 1)
            );
            break;
        case 'day':
        case 'date':
            time = startOfDate(this.year(), this.month(), this.date());
            break;
        case 'hour':
            time = this._d.valueOf();
            time -= mod$1(
                time + (this._isUTC ? 0 : this.utcOffset() * MS_PER_MINUTE),
                MS_PER_HOUR
            );
            break;
        case 'minute':
            time = this._d.valueOf();
            time -= mod$1(time, MS_PER_MINUTE);
            break;
        case 'second':
            time = this._d.valueOf();
            time -= mod$1(time, MS_PER_SECOND);
            break;
    }

    this._d.setTime(time);
    hooks.updateOffset(this, true);
    return this;
}