William Cheung willy-wagtail

## TS - More precise return type method Date#toISOString.d.ts
// In TS, interfaces are "open" and can be extended
interface Date {
  /**
   * Give a more precise return type to the method `toISOString()`:
   * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/toISOString
   */
  toISOString(): TDateISO;
}

type TYear         = `${number}${number}${number}${number}`;
	// In TS, interfaces are "open" and can be extended
	interface Date {
	/**
	* Give a more precise return type to the method `toISOString()`:
	* https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/toISOString
	*/
	toISOString(): TDateISO;
	}

	type TYear = `${number}${number}${number}${number}`;