JavaScript version
getWeekday.js
// `date` is a Date object
const getWeekday = (date) =>
['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'][date.getDay()];
TypeScript version
getWeekday.ts
const getWeekday = (date: Date): string =>
['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'][date.getDay()];