The names of the days of the week using browser locale

weekday-names.js

const anArbitrarySundayEarlyInTheMonth = new Date(2020, 0, 5)
const dayNumbers = [ 0, 1, 2, 3, 4, 5, 6 ]
const formatter = new Intl.DateTimeFormat(undefined, {
	weekday: `short`,
})

const weekdayNames = dayNumbers.map(dayNumber => {
	const date = new Date(anArbitrarySundayEarlyInTheMonth)
	date.setDate(date.getDate() + dayNumber)
	return formatter.format(date)
})