# Find next instance of a given weekday (ie. Monday) with moment.js

I want to get the date of the next Monday or Thursday (or today if it is Mon or Thurs). As Moment.js works within the bounds of a Sunday - Saturday, I'm having to work out the current day and calculate the next Monday or Thursday based on that:

``````if (moment().format("dddd")=="Sunday") { var nextDay = moment().day(1); }
if (moment().format("dddd")=="Monday") { var nextDay = moment().day(1); }
if (moment().format("dddd")=="Tuesday") { var nextDay = moment().day(4); }
if (moment().format("dddd")=="Wednesday") { var nextDay = moment().day(4); }
if (moment().format("dddd")=="Thursday") { var nextDay = moment().day(4); }
if (moment().format("dddd")=="Friday") { var nextDay = moment(.day(8); }
if (moment().format("dddd")=="Saturday") { var nextDay = moment().day(8); }
``````

This works, but surely there's a better way! The trick here isn't in using Moment to go to a particular day from today. It's generalizing it, so you can use it with any day, regardless of where you are in the week.

First you need to know where you are in the week: `moment.day()`, or the slightly more predictable (in spite of locale) `moment().isoWeekday()`. Critically, these methods return an integer, which makes it easy to use comparison operators to determine where you are in the week, relative to your targets.

Use that to know if today's day is smaller or bigger than the day you want. If it's smaller/equal, you can simply use this week's instance of Monday or Thursday...

``````const dayINeed = 4; // for Thursday
const today = moment().isoWeekday();

if (today <= dayINeed) {
return moment().isoWeekday(dayINeed);
}
``````

But, if today is bigger than the day we want, you want to use the same day of next week: "the monday of next week", regardless of where you are in the current week. In a nutshell, you want to first go into next week, using `moment().add(1, 'weeks')`. Once you're in next week, you can select the day you want, using `moment().day(1)`.

Together:

``````const dayINeed = 4; // for Thursday
const today = moment().isoWeekday();

// if we haven't yet passed the day of the week that I need:
if (today <= dayINeed) {
// then just give me this week's instance of that day
return moment().isoWeekday(dayINeed);
} else {
// otherwise, give me *next week's* instance of that same day
}
``````

EDIT: other commenters have pointed out that the OP wanted something more specific than this: the next of an array of values ("the next Monday or Thursday"), not merely the next instance of some arbitrary day. OK, cool.

The general solution is the beginning of the total solution. Instead of comparing for a single day, we're comparing to an array of days: `[1,4]`:

``````const daysINeed = [1,4]; // Monday, Thursday
// we will assume the days are in order for this demo, but inputs should be sanitized and sorted

function isThisInFuture(targetDayNum) {
// param: positive integer for weekday
// returns: matching moment or false
const todayNum = moment().isoWeekday();

if (todayNum <= targetDayNum) {
return moment().isoWeekday(targetDayNum);
}
return false;
}

function findNextInstanceInDaysArray(daysArray) {
// iterate the array of days and find all possible matches
const tests = daysINeed.map(isThisInFuture);

// select the first matching day of this week, ignoring subsequent ones, by finding the first moment object
const thisWeek = tests.find((sample) => {return sample instanceof moment});

// but if there are none, we'll return the first valid day of next week (again, assuming the days are sorted)
}
findNextInstanceInDaysArray(daysINeed);
``````

I'll note that some later posters provided a very lean solution that hard-codes an array of valid numeric values. If you always expect to search the same days, and don't need to generalize for other searches, that'll be the more computationally efficient solution, although not the easiest to read, and impossible to extend. get the next monday using moment

``````moment().startOf('isoWeek').add(1, 'week');
`````` `moment().day()` will give you a number referring to the day_of_week.

What's even better: `moment().day(1 + 7)` and `moment().day(4 + 7)` will give you next Monday, next Thursday respectively. The following can be used to get any next weekday date from now (or any date)

``````var weekDayToFind = moment().day('Monday').weekday(); //change to searched day name

var searchDate = moment(); //now or change to any date
while (searchDate.weekday() !== weekDayToFind){
}
`````` IMHO more elegant way:

``````var setDays = [ 1, 1, 4, 4, 4, 8, 8 ],
nextDay = moment().day( setDays[moment().day()] );
`````` Most of these answers do not address the OP's question. Andrejs Kuzmins' is the best, but I would improve on it a little more so the algorithm accounts for locale.

``````var nextMoOrTh = moment().isoWeekday([1,4,4,4,8,8,8][moment().isoWeekday()-1]);
`````` Here's e.g. next Monday:

``````var chosenWeekday = 1 // Monday

var nextChosenWeekday = chosenWeekday < moment().weekday() ? moment().weekday(chosenWeekday + 7) : moment().weekday(chosenWeekday)
`````` Next Monday or any other day

``````moment().startOf('isoWeek').add(1, 'week').day("monday");
`````` Here's a solution to find the next Monday, or today if it is Monday:

``````const dayOfWeek = moment().day('monday').hour(0).minute(0).second(0);

const endOfToday = moment().hour(23).minute(59).second(59);

if(dayOfWeek.isBefore(endOfToday)) {
}
`````` The idea is similar to the one of XML, but avoids the if / else statement by simply adding the missing days to the current day.

``````const desiredWeekday = 4; // Thursday
const currentWeekday = moment().isoWeekday();
const missingDays = ((desiredWeekday - currentWeekday) + 7) % 7;
``````

We only go "to the future" by ensuring that the days added are between 0 and 6. ``````// pick a day e.g. Mon = 1, if today is Mon returns next Mon
let d = 1
let future_date = moment().add( moment().day() >= d ? 7 - moment().day() + d : d - moment().day(), 'days' )
``````