Add helper to get the normalized day index on DateTime

src/datetime-class.js

@@ -1,8 +1,16 @@
 import { MILLISECONDS_PER_WEEK } from './utils/const.js'
 import { datetime, weekNumber } from './index.js'
+import { getNormalizeDay } from './utils/date.js'
 
 export class DateTime extends Date {
 
+  /**
+   * Get the day index of the week, except Sunday is 7 instead of 0.
+   *
+   * @returns {number}
+   */
+  getNormalisedDay = () => getNormalizeDay(this)
+
   /**
    * Returns the week of the year (`1`–`53`) of the specified date according to
    * local time, as defined by the WHATWG and the ISO-8601 specs:

src/datetime-class.test.js

@@ -45,6 +45,8 @@ describe('DateTime class', () => {
     })
   })
 
+  describe.todo('.getNormalisedDay()', () => {})
+
   describe('.getWeek()', () => {
 
     test('returns the week number', () => {