JavaScript - day name for the first day of month

In this article, we would like to show you how to get the first day name of the indicated month in JavaScript.

Quick solution:

// ONLINE-RUNNER:browser;

const days = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'];

const year = 2021;
const month = 7;   // 0 - January, ..., 7 - August, ..., 11 - December

const date = new Date(year, month, 1);
const day = days[date.getDay()];

console.log(day);  // Sunday

Where in the above code, we:

1. use an array with names of the weekdays,
2. create a date that represents the first day in the month - it is Date(year, month, 1),
3. get day index in the week using getDay() method - it counts days from 0 to 6, staring from Sunday,
4. get the day name from the array using the day index.

Reusable code example

// ONLINE-RUNNER:browser;

const days = ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'];

const getFirstDayName = (year, month) => {
	const date = new Date(year, month, 1); // first day of the month
  	return days[date.getDay()]; // getting day of the week (counted from 0 to 6 - Sunday as first)
};


// Usage example:

console.log(getFirstDayName(2021, 0));  // Friday  // 0 - January
console.log(getFirstDayName(2021, 1));  // Monday  // 1 - February
console.log(getFirstDayName(2021, 2));  // Monday  // 2 - March

Output:

Friday
Monday
Monday

See also

1. JavaScript - English day names

References

1. Date() constructor syntax - JavaScript