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JavaScript application for showing the weekend dates?

I thought a lot - I tried but I could not solve it. I need a JavaScript application that shows the nearest weekend dates in the current date.
If it's a weekend now, give it the dates of this weekend, if not, then next weekend's dates.
I'm waiting for your help.
Respects.

You can use the built-in Date constructor.
var date = new Date();
var day = date.getDay();
var saturday;
var sunday;
if(day === 0 || day === 6){ //0 for Sunday, 6 for Saturday
saturday = date;
sunday = new Date(saturday.getTime());
sunday.setDate(saturday.getDate() + (day === 0 ? -1 : 1));
if(day === 0){
var temp = saturday;
saturday = sunday; //Confusing, but they are actually the wrong dates, so we are switching the dates
sunday = temp;
temp = null; //Free up some memory!
}
}
else{
//This is the complicated part, we need to find when is the next Saturday
saturday = new Date(date.getFullYear(), date.getMonth(), (date.getDate() + 6) - day);
sunday = new Date(saturday.getTime());
sunday.setDate(saturday.getDate() + (saturday.getDay() === 0 ? -1 : 1));
}
date = day = null; //Free up some memory!
document.body.innerText = [saturday, sunday];
To get the date, use saturday.getDate() or sunday.getDate().Remember that Date months are 0-based. See here for more info.

var chosenDay = new Date();
var box = [];
var counting = 0;
for (var i = 0; i < 7; i++) {
chosenDay.setDate(chosenDay.getDate() + counting);
var day = chosenDay.getDate();
var dayy = chosenDay.getDay();
var month = chosenDay.getMonth()+1;
var year = chosenDay.getFullYear();
box.push({day: day, dayy: dayy});
counting = 1;
};
Now to find Saturday and Sunday
box.map(function(obj) {
if (obj.dayy === 6) {
console.log('Saturday found');
alert(obj.day);
};
if (obj.dayy === 0) {
console.log('Sunday found');
alert(obj.day);
};
});

I interpret the "nearest" weekend as being the previous weekend for Monday and Tuesday, and the next weekend for Thursday and Friday. You didn't provide any information on what to do with Wednesday.
However, from other answers it seems you want either the current weekend for Saturday and Sunday and or the next weekend for weekdays.
The following is a little more concise than other answers:
/* Get nearest weekend to the provided date
** #param {Date} date - date to get weekends nearst to
** #returns {Array} array of Dates [Saturday, Sunday]
*/
function getNearestWeekend(date) {
// Copy date so don't mess with provided date
var d = new Date(+date);
// If weekday, move d to next Saturday else to current weekend Saturday
if (d.getDay() % 6) {
d.setDate(d.getDate() + 6 - d.getDay());
} else {
d.setDate(d.getDate() - (d.getDay()? 0 : 1));
}
// Return array with Dates for Saturday, Sunday
return [new Date(d), new Date(d.setDate(d.getDate() + 1))]
}
// Some tests
[new Date(2017,0,7), // Sat 7 Jan
new Date(2017,0,8), // Sun 8 Jan
new Date(2017,0,9), // Mon 9 Jan
new Date(2017,0,12) // Thu 12 Jan
].forEach(function(d) {
var opts = {weekday:'short', day:'numeric', month:'short'};
console.log('Date: ' + d.toLocaleString('en-GB',opts) + ' | Next weekend: ' +
getNearestWeekend(d).map(d =>d.toLocaleString('en-GB',opts)).join(' and ')
);
});

How to check if date is in this week in javascript?

I have this date "2016-04-23T11:45:00Z" and I want to check this date in this week or not ?
Thanks,

Dates are hard, I would always suggest using a library dedicated to date handling as it reduces the chances of errors in your code.
MomentJS is a good one.
var now = moment();
var input = moment("2016-04-17T11:45:00Z");
var isThisWeek = (now.isoWeek() == input.isoWeek())
Edit: Please note as of 2020 moment may not be a good choice for new projects

This seems to be working for me.
function isDateInThisWeek(date) {
const todayObj = new Date();
const todayDate = todayObj.getDate();
const todayDay = todayObj.getDay();
// get first date of week
const firstDayOfWeek = new Date(todayObj.setDate(todayDate - todayDay));
// get last date of week
const lastDayOfWeek = new Date(firstDayOfWeek);
lastDayOfWeek.setDate(lastDayOfWeek.getDate() + 6);
// if date is equal or within the first and last dates of the week
return date >= firstDayOfWeek && date <= lastDayOfWeek;
}
const date = new Date();
const isInWeek = isDateInThisWeek(date);

<div ng-app="myApp">
<div class="container" ng-controller="Ctrl_List">
<h1>{{currentDate}}</h1>
<h1>{{numberCurrentDateWeeks}}</h1>
<h1>{{yourDate}}</h1>
<h1>{{numberYourDateWeeks}}</h1>
</div>
</div>
......
angular.module('myApp', [])
.controller("Ctrl_List", ["$scope", "$filter", function(s, $filter) {
s.yourDate = '2016-04-23T11:45:00Z'
s.currentDate = new Date();
s.numberCurrentDateWeeks = $filter('date')(s.currentDate, "w");
s.numberYourDateWeeks = $filter('date')(s.yourDate, "w");
}]);
then you got the Week numbers just compare or do whatever you like
cheers !

You can do that without any libraries by checking if the date.getTime() (milliseconds since epoch) is between last monday and next monday:
const WEEK_LENGTH = 604800000;
function onCurrentWeek(date) {
var lastMonday = new Date(); // Creating new date object for today
lastMonday.setDate(lastMonday.getDate() - (lastMonday.getDay()-1)); // Setting date to last monday
lastMonday.setHours(0,0,0,0); // Setting Hour to 00:00:00:00
const res = lastMonday.getTime() <= date.getTime() &&
date.getTime() < ( lastMonday.getTime() + WEEK_LENGTH);
return res; // true / false
}
(one week in ms = 24 * 60 * 60 * 1000 * 7 = 604,800,000)

May not be the most optimal solution, but I think it's quite readable:
function isThisWeek (date) {
const now = new Date();
const weekDay = (now.getDay() + 6) % 7; // Make sure Sunday is 6, not 0
const monthDay = now.getDate();
const mondayThisWeek = monthDay - weekDay;
const startOfThisWeek = new Date(+now);
startOfThisWeek.setDate(mondayThisWeek);
startOfThisWeek.setHours(0, 0, 0, 0);
const startOfNextWeek = new Date(+startOfThisWeek);
startOfNextWeek.setDate(mondayThisWeek + 7);
return date >= startOfThisWeek && date < startOfNextWeek;
}

This link explaines, how to do this without using any js libraries. https://gist.github.com/dblock/1081513
Code against link death:
function( d ) {
// Create a copy of this date object
var target = new Date(d.valueOf());
// ISO week date weeks start on monday
// so correct the day number
var dayNr = (d.getDay() + 6) % 7;
// Set the target to the thursday of this week so the
// target date is in the right year
target.setDate(target.getDate() - dayNr + 3);
// ISO 8601 states that week 1 is the week
// with january 4th in it
var jan4 = new Date(target.getFullYear(), 0, 4);
// Number of days between target date and january 4th
var dayDiff = (target - jan4) / 86400000;
// Calculate week number: Week 1 (january 4th) plus the
// number of weeks between target date and january 4th
var weekNr = 1 + Math.ceil(dayDiff / 7);
return weekNr;
}

I managed to do it with this simple trick and without any external library.
Considering monday as the first day of the week, the function takes as parameter a date string and do the validation before checking if the day indeed is in the current week.
function isInThisWeek(livr){
const WEEK = new Date()
// convert delivery date to Date instance
const DATEREF = new Date(livr)
// Check if date instance is in valid format (depends on the function arg)
if(DATEREF instanceof Date && isNaN(DATEREF)){
console.log("invalid date format")
return false}
// Deconstruct to get separated date infos
const [dayR, monthR, yearR] = [DATEREF.getDate(), DATEREF.getMonth(), DATEREF.getFullYear()]
// get Monday date
const monday = (WEEK.getDate() - WEEK.getDay()) + 1
// get Saturday date
const sunday = monday + 6
// Start verification
if (yearR !== WEEK.getFullYear()) { console.log("WRONG YEAR"); return false }
if (monthR !== WEEK.getMonth()) { console.log("WRONG MONTH"); return false }
if(dayR >= monday && dayR <= sunday) { return true }
else {console.log("WRONG DAY"); return false}
}

In the comments I saw that you stated that your week starts on Monday.
In that case, I guess it'd be a good idea to calculate the ISO week number of the 2 dates and see if you get the same week number for both of them.
To calculate the ISO week number, check this answer:
In case anyone else's week starts on Sunday instead, you can use this answer to calculate the week number accordingly.
then you can do something like this:
function isSameWeek(date1, date2) {
return date1.getWeekNumber() === date2.getWeekNumber();
}

const isDateInThisWeek = (date) => {
const today = new Date();
//Get the first day of the current week (Sunday)
const firstDayOfWeek = new Date(
today.setDate(today.getDate() - today.getDay())
);
//Get the last day of the current week (Saturday)
const lastDayOfWeek = new Date(
today.setDate(today.getDate() - today.getDay() + 6)
);
//check if my value is between a minimum date and a maximum date
if (date >= firstDayOfWeek && date <= lastDayOfWeek) {
return true;
} else {
return false;
}
};

Moment.js how to get week of month? (google calendar style)

I am using Moment.js and it is great. The problem I have now is that I can't figure out how to get the week of the month a certain date is. I can only find "week of year" in the Moment js docs. For example, if I choose today's date (2/12/2014), I would like to know that this date is in the second week of this month of february and consequently, it is the second wednesday of the month. Any ideas?
EDIT:
I guess some clarification is necessary. What I need most is the nth number of a certain day in a month. For example, (from the comments) Feb 1, 2014 would be the first Saturday of the month. Feb 3, 2014 would be the first Monday of the month even though it is "technically" the second week of the month. Basically, exactly how google calendar's repeat function classifies days.

It seems that moment.js does not have the method that implements the functionality that you are looking for.
However, you can find the nth number of a certain day of the week in a month is using the Math.ceil of the date / 7
For example:
var firstFeb2014 = moment("2014-02-01"); //saturday
var day = firstFeb2014.day(); //6 = saturday
var nthOfMoth = Math.ceil(firstFeb2014.date() / 7); //1
var eightFeb2014 = moment("2014-02-08"); //saturday, the next one
console.log( Math.ceil(eightFeb2014.date() / 7) ); //prints 2, as expected
It looks like this is the number you are looking for, as demonstrated by the following test
function test(mJsDate){
var str = mJsDate.toLocaleString().substring(0, 3) +
" number " + Math.ceil(mJsDate.date() / 7) +
" of the month";
return str;
}
for(var i = 1; i <= 31; i++) {
var dayStr = "2014-01-"+ i;
console.log(dayStr + " " + test(moment(dayStr)) );
}
//examples from the console:
//2014-01-8 Wed number 2 of the month
//2014-01-13 Mon number 2 of the month
//2014-01-20 Mon number 3 of the month
//2014-01-27 Mon number 4 of the month
//2014-01-29 Wed number 5 of the month

When calculating the week of the month based on a given date, you have to take the offset into account. Not all months start on the first day of the week.
If you want to take this offset into account, you can use something something like the following if you are using moment.
function weekOfMonth (input = moment()) {
const firstDayOfMonth = input.clone().startOf('month');
const firstDayOfWeek = firstDayOfMonth.clone().startOf('week');
const offset = firstDayOfMonth.diff(firstDayOfWeek, 'days');
return Math.ceil((input.date() + offset) / 7);
}

Simple using moment.js
function week_of_month(date) {
prefixes = [1,2,3,4,5];
return prefixes[0 | moment(date).date() / 7]
}

This library adds the function moment.weekMonth()
https://github.com/c-trimm/moment-recur

I made some modifications based on feedback.
let weeks = moment().weeks() - moment().startOf('month').weeks() + 1;
weeks = (weeks + 52) % 52;
On days passing through the next year, the week value will be negative so I had to add 52.

What about something like:
weekOfCurrentMonth = (moment().week() - (moment().month()*4));
This takes the current week of the year, and subtracts it by the 4 times the number of previous months. Which should give you the week of the current month

I think the answer to this question will be helpful, even though it doesn't use moment.js as requested:
Get week of the month

function countWeekdayOccurrencesInMonth(date) {
var m = moment(date),
weekDay = m.day(),
yearDay = m.dayOfYear(),
count = 0;
m.startOf('month');
while (m.dayOfYear() <= yearDay) {
if (m.day() == weekDay) {
count++;
}
m.add('days', 1);
}
return count;
}

There is a problem with #Daniel Earwicker answer.
I was using his function in my application and the while loop was infinite because of the following situation:
I was trying to figure out which week of december (2016) was the day 31.
the first day of december was day 336 of the year. The last day of december was day 366 of the year.
Problem here: When it was day 366 (31 of december, last day of the year) the code added another day to this date. But with another day added it would be day 1 of january of 2017. Therefore the loop never ended.
while (m.dayOfYear() <= yearDay) {
if (m.day() == weekDay) {
count++;
}
m.add('days', 1);
}
I added the following lines to the code so the problem would be fixed:
function countWeekdayOccurrencesInMonth(date) {
var m = moment(date),
weekDay = m.day(),
yearDay = m.dayOfYear(),
year = m.year(),
count = 0;
m.startOf('month');
while (m.dayOfYear() <= yearDay && m.year() == year) {
if (m.day() == weekDay) {
count++;
}
m.add('days', 1);
}
return count;
}
It verifies if it is still in the same year of the date being veryfied

Here's Robin Malfait's solution implemented with the lightweight library date-fns
import {
differenceInDays,
startOfMonth,
startOfWeek,
getDate
} from 'date-fns'
const weekOfMonth = function (date) {
const firstDayOfMonth = startOfMonth(date)
const firstDayOfWeek = startOfWeek(firstDayOfMonth)
const offset = differenceInDays(firstDayOfMonth, firstDayOfWeek)
return Math.ceil((getDate(date) + offset) / 7)
}
export default weekOfMonth

I'd do the following:
let todaysDate = moment(moment.now());
let endOfLastMonth = moment(get(this, 'todaysDate')).startOf('month').subtract(1, 'week');
let weekOfMonth = todaysDate.diff(endOfLastMonth, 'weeks');
That gets todaysDate and the endOfLastMonth and then uses Moment's built-in diff() method to compute the current month's week number.

It's not built-in, but basically you can subtract the week number of the start of the month from the week number of the date in question.
function weekOfMonth(m) {
return m.week() - moment(m).startOf('month').week() + 1;
}
Credit goes to code by original author, give him a star if it helped you.

How about this?
const moment = require("moment");
// Generate Week Number of The Month From Moment Date
function getWeekOfMonth(input = moment()) {
let dayOfInput = input.clone().day(); // Saunday is 0 and Saturday is 6
let diffToNextWeek = 7 - dayOfInput;
let nextWeekStartDate = input.date() + diffToNextWeek;
return Math.ceil((nextWeekStartDate) / 7);
}

Simple code, but has been working for me.
const weekOfTheMonth = (myMomentDate) => {
const startDay = moment(myMomentDate).startOf('week');
const day = parseInt(startDay.format('DD'),10);
if(day > 28){
return 5;
}
if((day > 21) && (day <= 28) ){
return 4;
}
if((day > 14) && (day <= 21) ){
return 3;
}
if((day > 7) && (day <= 14) ){
return 2;
}
return 1;
}

JavaScript - get the first day of the week from current date

I need the fastest way to get the first day of the week. For example: today is the 11th of November, and a Thursday; and I want the first day of this week, which is the 8th of November, and a Monday. I need the fastest method for MongoDB map function, any ideas?

Using the getDay method of Date objects, you can know the number of day of the week (being 0=Sunday, 1=Monday, etc).
You can then subtract that number of days plus one, for example:
function getMonday(d) {
d = new Date(d);
var day = d.getDay(),
diff = d.getDate() - day + (day == 0 ? -6:1); // adjust when day is sunday
return new Date(d.setDate(diff));
}
getMonday(new Date()); // Mon Nov 08 2010

Not sure how it compares for performance, but this works.
var today = new Date();
var day = today.getDay() || 7; // Get current day number, converting Sun. to 7
if( day !== 1 ) // Only manipulate the date if it isn't Mon.
today.setHours(-24 * (day - 1)); // Set the hours to day number minus 1
// multiplied by negative 24
alert(today); // will be Monday
Or as a function:
# modifies _date_
function setToMonday( date ) {
var day = date.getDay() || 7;
if( day !== 1 )
date.setHours(-24 * (day - 1));
return date;
}
setToMonday(new Date());

CMS's answer is correct but assumes that Monday is the first day of the week.
Chandler Zwolle's answer is correct but fiddles with the Date prototype.
Other answers that add/subtract hours/minutes/seconds/milliseconds are wrong because not all days have 24 hours.
The function below is correct and takes a date as first parameter and the desired first day of the week as second parameter (0 for Sunday, 1 for Monday, etc.). Note: the hour, minutes and seconds are set to 0 to have the beginning of the day.
function firstDayOfWeek(dateObject, firstDayOfWeekIndex) {
const dayOfWeek = dateObject.getDay(),
firstDayOfWeek = new Date(dateObject),
diff = dayOfWeek >= firstDayOfWeekIndex ?
dayOfWeek - firstDayOfWeekIndex :
6 - dayOfWeek
firstDayOfWeek.setDate(dateObject.getDate() - diff)
firstDayOfWeek.setHours(0,0,0,0)
return firstDayOfWeek
}
// August 18th was a Saturday
let lastMonday = firstDayOfWeek(new Date('August 18, 2018 03:24:00'), 1)
// outputs something like "Mon Aug 13 2018 00:00:00 GMT+0200"
// (may vary according to your time zone)
document.write(lastMonday)

First / Last Day of The Week
To get the upcoming first day of the week, you can use something like so:
function getUpcomingSunday() {
const date = new Date();
const today = date.getDate();
const currentDay = date.getDay();
const newDate = date.setDate(today - currentDay + 7);
return new Date(newDate);
}
console.log(getUpcomingSunday());
Or to get the latest first day:
function getLastSunday() {
const date = new Date();
const today = date.getDate();
const currentDay = date.getDay();
const newDate = date.setDate(today - (currentDay || 7));
return new Date(newDate);
}
console.log(getLastSunday());
* Depending on your time zone, the beginning of the week doesn't has to start on Sunday, it can start on Friday, Saturday, Monday or any other day your machine is set to. Those methods will account for that.
* You can also format it using toISOString method like so: getLastSunday().toISOString()

Check out Date.js
Date.today().previous().monday()

var dt = new Date(); // current date of week
var currentWeekDay = dt.getDay();
var lessDays = currentWeekDay == 0 ? 6 : currentWeekDay - 1;
var wkStart = new Date(new Date(dt).setDate(dt.getDate() - lessDays));
var wkEnd = new Date(new Date(wkStart).setDate(wkStart.getDate() + 6));
This will work well.

I'm using this
function get_next_week_start() {
var now = new Date();
var next_week_start = new Date(now.getFullYear(), now.getMonth(), now.getDate()+(8 - now.getDay()));
return next_week_start;
}

Returns Monday 00am to Monday 00am.
const now = new Date()
const startOfWeek = new Date(now.getFullYear(), now.getMonth(), now.getDate() - now.getDay() + 1)
const endOfWeek = new Date(now.getFullYear(), now.getMonth(), startOfWeek.getDate() + 7)

This function uses the current millisecond time to subtract the current week, and then subtracts one more week if the current date is on a monday (javascript counts from sunday).
function getMonday(fromDate) {
// length of one day i milliseconds
var dayLength = 24 * 60 * 60 * 1000;
// Get the current date (without time)
var currentDate = new Date(fromDate.getFullYear(), fromDate.getMonth(), fromDate.getDate());
// Get the current date's millisecond for this week
var currentWeekDayMillisecond = ((currentDate.getDay()) * dayLength);
// subtract the current date with the current date's millisecond for this week
var monday = new Date(currentDate.getTime() - currentWeekDayMillisecond + dayLength);
if (monday > currentDate) {
// It is sunday, so we need to go back further
monday = new Date(monday.getTime() - (dayLength * 7));
}
return monday;
}
I have tested it when week spans over from one month to another (and also years), and it seems to work properly.

Good evening,
I prefer to just have a simple extension method:
Date.prototype.startOfWeek = function (pStartOfWeek) {
var mDifference = this.getDay() - pStartOfWeek;
if (mDifference < 0) {
mDifference += 7;
}
return new Date(this.addDays(mDifference * -1));
}
You'll notice this actually utilizes another extension method that I use:
Date.prototype.addDays = function (pDays) {
var mDate = new Date(this.valueOf());
mDate.setDate(mDate.getDate() + pDays);
return mDate;
};
Now, if your weeks start on Sunday, pass in a "0" for the pStartOfWeek parameter, like so:
var mThisSunday = new Date().startOfWeek(0);
Similarly, if your weeks start on Monday, pass in a "1" for the pStartOfWeek parameter:
var mThisMonday = new Date().startOfWeek(1);
Regards,

a more generalized version of this... this will give you any day in the current week based on what day you specify.
//returns the relative day in the week 0 = Sunday, 1 = Monday ... 6 = Saturday
function getRelativeDayInWeek(d,dy) {
d = new Date(d);
var day = d.getDay(),
diff = d.getDate() - day + (day == 0 ? -6:dy); // adjust when day is sunday
return new Date(d.setDate(diff));
}
var monday = getRelativeDayInWeek(new Date(),1);
var friday = getRelativeDayInWeek(new Date(),5);
console.log(monday);
console.log(friday);

Simple solution for getting the first day of the week.
With this solution, it is possible to set an arbitrary start of week (e.g. Sunday = 0, Monday = 1, Tuesday = 2, etc.).
function getBeginOfWeek(date = new Date(), startOfWeek = 1) {
const result = new Date(date);
while (result.getDay() !== startOfWeek) {
result.setDate(result.getDate() - 1);
}
return result;
}
The solution correctly wraps on months (due to Date.setDate() being used)
For startOfWeek, the same constant numbers as in Date.getDay() can be used

setDate() has issues with month boundaries that are noted in comments above. A clean workaround is to find the date difference using epoch timestamps rather than the (surprisingly counterintuitive) methods on the Date object. I.e.
function getPreviousMonday(fromDate) {
var dayMillisecs = 24 * 60 * 60 * 1000;
// Get Date object truncated to date.
var d = new Date(new Date(fromDate || Date()).toISOString().slice(0, 10));
// If today is Sunday (day 0) subtract an extra 7 days.
var dayDiff = d.getDay() === 0 ? 7 : 0;
// Get date diff in millisecs to avoid setDate() bugs with month boundaries.
var mondayMillisecs = d.getTime() - (d.getDay() + dayDiff) * dayMillisecs;
// Return date as YYYY-MM-DD string.
return new Date(mondayMillisecs).toISOString().slice(0, 10);
}

Here is my solution:
function getWeekDates(){
var day_milliseconds = 24*60*60*1000;
var dates = [];
var current_date = new Date();
var monday = new Date(current_date.getTime()-(current_date.getDay()-1)*day_milliseconds);
var sunday = new Date(monday.getTime()+6*day_milliseconds);
dates.push(monday);
for(var i = 1; i < 6; i++){
dates.push(new Date(monday.getTime()+i*day_milliseconds));
}
dates.push(sunday);
return dates;
}
Now you can pick date by returned array index.

An example of the mathematically only calculation, without any Date functions.
const date = new Date();
const ts = +date;
const mondayTS = ts - ts % (60 * 60 * 24 * (7-4) * 1000);
const monday = new Date(mondayTS);
console.log(monday.toISOString(), 'Day:', monday.getDay());
const formatTS = v => new Date(v).toISOString();
const adjust = (v, d = 1) => v - v % (d * 1000);
const d = new Date('2020-04-22T21:48:17.468Z');
const ts = +d; // 1587592097468
const test = v => console.log(formatTS(adjust(ts, v)));
test(); // 2020-04-22T21:48:17.000Z
test(60); // 2020-04-22T21:48:00.000Z
test(60 * 60); // 2020-04-22T21:00:00.000Z
test(60 * 60 * 24); // 2020-04-22T00:00:00.000Z
test(60 * 60 * 24 * (7-4)); // 2020-04-20T00:00:00.000Z, monday
// So, what does `(7-4)` mean?
// 7 - days number in the week
// 4 - shifting for the weekday number of the first second of the 1970 year, the first time stamp second.
// new Date(0) ---> 1970-01-01T00:00:00.000Z
// new Date(0).getDay() ---> 4

It is important to discern between local time and UTC. I wanted to find the start of the week in UTC, so I used the following function.
function start_of_week_utc(date, start_day = 1) {
// Returns the start of the week containing a 'date'. Monday 00:00 UTC is
// considered to be the boundary between adjacent weeks, unless 'start_day' is
// specified. A Date object is returned.
date = new Date(date);
const day_of_month = date.getUTCDate();
const day_of_week = date.getUTCDay();
const difference_in_days = (
day_of_week >= start_day
? day_of_week - start_day
: day_of_week - start_day + 7
);
date.setUTCDate(day_of_month - difference_in_days);
date.setUTCHours(0);
date.setUTCMinutes(0);
date.setUTCSeconds(0);
date.setUTCMilliseconds(0);
return date;
}
To find the start of the week in a given timezone, first add the timezone offset to the input date and then subtract it from the output date.
const local_start_of_week = new Date(
start_of_week_utc(
date.getTime() + timezone_offset_ms
).getTime() - timezone_offset_ms
);

I use this:
let current_date = new Date();
let days_to_monday = 1 - current_date.getDay();
monday_date = current_date.addDays(days_to_monday);
// https://stackoverflow.com/a/563442/6533037
Date.prototype.addDays = function(days) {
var date = new Date(this.valueOf());
date.setDate(date.getDate() + days);
return date;
}
It works fine.

Accepted answer won't work for anyone who runs the code in UTC-XX:XX timezone.
Here is code which will work regardless of timezone for date only. This won't work if you provide time too. Only provide date or parse date and provide it as input. I have mentioned different test cases at start of the code.
function getDateForTheMonday(dateString) {
var orignalDate = new Date(dateString)
var modifiedDate = new Date(dateString)
var day = modifiedDate.getDay()
diff = modifiedDate.getDate() - day + (day == 0 ? -6:1);// adjust when day is sunday
modifiedDate.setDate(diff)
var diffInDate = orignalDate.getDate() - modifiedDate.getDate()
if(diffInDate == 6) {
diff = diff + 7
modifiedDate.setDate(diff)
}
console.log("Given Date : " + orignalDate.toUTCString())
console.log("Modified date for Monday : " + modifiedDate)
}
getDateForTheMonday("2022-08-01") // Jul month with 31 Days
getDateForTheMonday("2022-07-01") // June month with 30 days
getDateForTheMonday("2022-03-01") // Non leap year February
getDateForTheMonday("2020-03-01") // Leap year February
getDateForTheMonday("2022-01-01") // First day of the year
getDateForTheMonday("2021-12-31") // Last day of the year

Extending answer from #Christian C. Salvadó and information from #Ayyash (object is mutable) and #Awi and #Louis Ameline (set hours to 00:00:00)
The function can be like this
function getMonday(d) {
var day = d.getDay(),
diff = d.getDate() - day + (day == 0 ? -6:1); // adjust when day is sunday
d.setDate(diff);
d.setHours(0,0,0,0); // set hours to 00:00:00
return d; // object is mutable no need to recreate object
}
getMonday(new Date())

Check out: moment.js
Example:
moment().day(-7); // last Sunday (0 - 7)
moment().day(7); // next Sunday (0 + 7)
moment().day(10); // next Wednesday (3 + 7)
moment().day(24); // 3 Wednesdays from now (3 + 7 + 7 + 7)
Bonus: works with node.js too

Determine if a date is a Saturday or a Sunday using JavaScript

Is it possible to determine if a date is a Saturday or Sunday using JavaScript?
Do you have the code for this?

Sure it is! The Date class has a function called getDay() which returns a integer between 0 and 6 (0 being Sunday, 6 being Saturday). So, in order to see if today is during the weekend:
var today = new Date();
if(today.getDay() == 6 || today.getDay() == 0) alert('Weekend!');
In order to see if an arbitrary date is a weekend day, you can use the following:
var myDate = new Date();
myDate.setFullYear(2009);
myDate.setMonth(7);
myDate.setDate(25);
if(myDate.getDay() == 6 || myDate.getDay() == 0) alert('Weekend!');

You can simplify #Andrew Moore 's test even further:
if(!(myDate.getDay() % 6)) alert('Weekend!');
(Love that modulo function!)

The Date class offers the getDay() Method that retrieves the day of the week component of the date as a number from 0 to 6 (0=Sunday, 1=Monday, etc)
var date = new Date();
switch(date.getDay()){
case 0: alert("sunday!"); break;
case 6: alert("saturday!"); break;
default: alert("any other week day");
}

I think this is an elegant way to do this:
function showDay(d) {
return ["weekday", "weekend"][parseInt(d.getDay() / 6)];
}
console.log(showDay(new Date()));

Yes, it is possible, we can write a JavaScript code for that using JavaScript Date object.
Please use following JavaScript code.
var d = new Date()
document.write(d.getDay())
We can write a function to return the weekend in flag like below,
You can more customize the function to pass date. Or different return values for every day.
isItWeekEnd = function() {
var d = new Date();
console.log(d.getDay());
var dateValue = d.getDay();
// dateValue : 0 = Sunday
// dateValue : 6 = Saturday
if(dateValue == 0 || dateValue == 6)
return true;
else
return false;
}

var date = new Date();
var day = date.getDay();
if(day==0){
return false;
//alert('sunday');
}