code: function dateAdd (date, interval, units) {
    let result = new Date(date)
  
    switch (interval.toLowerCase()) {
      case 'year':
        result.setFullYear(result.getFullYear() + units)
        break
      case 'quarter':
        result.setMonth(result.getMonth() + 3 * units)
        break
      case 'month':
        result.setMonth(result.getMonth() + units)
        break
      case 'week':
        result.setDate(result.getDate() + 7 * units)
        break
      case 'day':
        result.setDate(result.getDate() + units)
        break
      case 'hour':
        result.setTime(result.getTime() + units * 3600000)
        break
      case 'minute':
        result.setTime(result.getTime() + units * 60000)
        break
      case 'second':
        result.setTime(result.getTime() + units * 1000)
        break
      default:
        result = undefined
        break
    }
    return result
  }
docs: Utility function to add units to date based on interval
  @param {Date} date
  @param {String} interval
  @param {Number} units