西暦日付に型定義

Date は エラーになるが stringよりは狭まったものがほしい

TL;DR;

const oneToNine = [1, 2, 3, 4, 5, 6, 7, 8, 9] as const;
const d = [0, ...oneToNine] as const;
type OneToNine = typeof oneToNine[number];
type D = typeof d[number];
type YYYY = `19${D}${D}` | `20${D}${D}`;
type MM = `0${OneToNine}` | `1${0 | 1 | 2}`;
type DD = `${0}${OneToNine}` | `${1 | 2}${D}` | `3${0 | 1}`;
// これを使う
export type DateYMDString = `${YYYY}/${MM}/${DD}`;

例

let sample1 : Date;
sample1 = '2021/05/27'
// => エラー
// Type 'string' is not assignable to type 'Date'

let sample1 : DateYMDString;
sample1 = '2021/05/27'
// => OK
sample1= '2020:05:27'
// => エラー
// Type '"2020:05:27"' is not assignable to type '"1900/01/01" | "1900/01/02" | "1900/01/03" | "1900/01/04" | "1900/01/05" | "1900/01/06" | "1900/01/07" | "1900/01/08" | "1900/01/09" | "1900/01/10" | "1900/01/11" | "1900/01/12" | ... 74387 more ... | "2099/12/31"'.