JavaScript get working days

Examples

Get the day of the week:

const d = new Date();
let day = d.getDay();

Get the day of the week of a specific date:

const d = new Date("July 21, 1983 01:15:00");
let day = d.getDay();

More examples below.

Definition and Usage

The getDay() method returns the day of the week (0 to 6) of a date.

Sunday = 0, Monday = 1, ... (See below):

Syntax

Parameters

Return Value

More Examples

Get the name of the weekday (not just a number):

const weekday = ["Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"];

const d = new Date();
let day = weekday[d.getDay()];

Browser Support

getDay() is an ECMAScript1 (ES1) feature.

ES1 (JavaScript 1997) is fully supported in all browsers:

The problem is that that does not give you an accurate count - you also need to allow for holidays, and working those out is a lot harder, and will vary from region to region.

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Sometimes when thinking about something I want to post, a particular part of it grabs my attention and I decide to rip it out and write something focused on just that one aspect. That's what happened today when I was thinking about a particular way of doing date math and I wanted to see if it would make sense.

Given a particular date, I want to add a certain number of days to it (or weeks, or months), but I want the result to "prefer" business days. This is not the same as adding business days. So for example, 20 days from now is pretty different from 20 business days from now. Rather, I want the main difference to be close to my desired duration, but just "adjusted" to fall on a business day.

To test out my theory that this was possible, I decided to use the date-fns date library.

date-fns has a wealth of useful date utilities, including a couple I'd need to implement my logic:

• add - lets you quickly add durations to dates
• isWeekend - returns true if a date falls on a weekends
• nextMonday - fires up a Web3 crypto miner via Docker and Lambda to generate machine-driven art. No, actually it just returns the next Monday after a date

I began with a simple function that takes an input date and a duration in days:

const addDayPreferBusinessDay = (date,numDays) => {
    let newDate = add(date, { days:numDays });
    if(isWeekend(newDate)) {
        newDate = nextMonday(newDate);
    }
    return newDate;
}

Pretty straightforward I think. I wrote a quick test that started with today and added 0 to 14 days. Here's how the results looked:

Fri 2022-09-23, plus 0 days, using addDayPreferBusinessDay: Fri 2022-09-23
Fri 2022-09-23, plus 1 days, using addDayPreferBusinessDay: Mon 2022-09-26
Fri 2022-09-23, plus 2 days, using addDayPreferBusinessDay: Mon 2022-09-26
Fri 2022-09-23, plus 3 days, using addDayPreferBusinessDay: Mon 2022-09-26
Fri 2022-09-23, plus 4 days, using addDayPreferBusinessDay: Tue 2022-09-27
Fri 2022-09-23, plus 5 days, using addDayPreferBusinessDay: Wed 2022-09-28
Fri 2022-09-23, plus 6 days, using addDayPreferBusinessDay: Thu 2022-09-29
Fri 2022-09-23, plus 7 days, using addDayPreferBusinessDay: Fri 2022-09-30
Fri 2022-09-23, plus 8 days, using addDayPreferBusinessDay: Mon 2022-10-03
Fri 2022-09-23, plus 9 days, using addDayPreferBusinessDay: Mon 2022-10-03
Fri 2022-09-23, plus 10 days, using addDayPreferBusinessDay: Mon 2022-10-03
Fri 2022-09-23, plus 11 days, using addDayPreferBusinessDay: Tue 2022-10-04
Fri 2022-09-23, plus 12 days, using addDayPreferBusinessDay: Wed 2022-10-05
Fri 2022-09-23, plus 13 days, using addDayPreferBusinessDay: Thu 2022-10-06
Fri 2022-09-23, plus 14 days, using addDayPreferBusinessDay: Fri 2022-10-07

Given that today is Friday, you can see how the next few days all bump to Monday, and do so again next week.

For the heck of it, I decided to compare this to strictly adding business days. date-fns has a function for this, ]addBusinessDays](https://date-fns.org/v2.29.3/docs/addBusinessDays). Here's how those results look:

Fri 2022-09-23, plus 0 days, using addBusinessDays: Fri 2022-09-23
Fri 2022-09-23, plus 1 days, using addBusinessDays: Mon 2022-09-26
Fri 2022-09-23, plus 2 days, using addBusinessDays: Tue 2022-09-27
Fri 2022-09-23, plus 3 days, using addBusinessDays: Wed 2022-09-28
Fri 2022-09-23, plus 4 days, using addBusinessDays: Thu 2022-09-29
Fri 2022-09-23, plus 5 days, using addBusinessDays: Fri 2022-09-30
Fri 2022-09-23, plus 6 days, using addBusinessDays: Mon 2022-10-03
Fri 2022-09-23, plus 7 days, using addBusinessDays: Tue 2022-10-04
Fri 2022-09-23, plus 8 days, using addBusinessDays: Wed 2022-10-05
Fri 2022-09-23, plus 9 days, using addBusinessDays: Thu 2022-10-06
Fri 2022-09-23, plus 10 days, using addBusinessDays: Fri 2022-10-07
Fri 2022-09-23, plus 11 days, using addBusinessDays: Mon 2022-10-10
Fri 2022-09-23, plus 12 days, using addBusinessDays: Tue 2022-10-11
Fri 2022-09-23, plus 13 days, using addBusinessDays: Wed 2022-10-12
Fri 2022-09-23, plus 14 days, using addBusinessDays: Thu 2022-10-13

I think you can really see, especially at the end, how things begin to diverge. Is my way "better"? For what I want to use it for, I think it is. Obviously, time will tell, and like always, I'd love to know if people think this is useful. Note I used another useful date-fns utility to render my dates, format

How to find working days in JavaScript?

How to get business days in JavaScript?

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How can I calculate working days?