Use .getDay() method on the Date object to get the day.
Check if it is 6 (Saturday) or 0 (Sunday)
var givenDate = new Date('2020-07-11');
var day = givenDate.getDay();
var isWeekend = (day === 6) || (day === 0) ? 'It's weekend': 'It's working day';
console.log(isWeekend);