dayName

Gets the name of the weekday from a Date object.

• Use Date.prototype.toLocaleDateString() with the { weekday: 'long' } option to retrieve the weekday.
• Use the optional second argument to get a language-specific name or omit it to use the default locale.

const dayName = (date, locale) =>
  date.toLocaleDateString(locale, { weekday: 'long' });

dayName(new Date()); // 'Saturday'
dayName(new Date('09/23/2020'), 'de-DE'); // 'Samstag'