isWeekday

Checks if the given date is a weekday.

• Use Date.prototype.getDay() to check weekday by using a modulo operator (%).
• Omit the argument, d, to use the current date as default.

const isWeekday = (d = new Date()) => d.getDay() % 6 !== 0;

isWeekday(); // true (if current date is 2019-07-19)