Transforming Date Fields in TypeScript Schemas

const DecodedObject = {
    id: Number,
    ...
    planDate: Date,
    factDate: Date
}

const EncodedObject = {
    id: string,
    ...
    planDate_year: number,
    planDate_month: number,
    planDate_day: number,

    factDate_year: number,
    factDate_month: number,
    factDate_day: number,
}

const DateFromYearMonthDayFields = Schema. <some transformation here>

const ObjectSchema = Schema.Struct({
  id: Schema.NumberFromString,
  dueDate: DateFromYearMonthDayFields,
  factDate: DateFromYearMonthDayFields
})