Is there a way to find the Nth occurrence of a specific weekday in each month between two given dates using JavaScript?

Question

Is there a way to find the Nth occurrence of a specific weekday in each month between two given dates using JavaScript?

Within my program, users can set events with start and end dates, as well as the period of repetition: weekly, monthly by date, monthly by weekday, or yearly. Once an event is created, it's stored in the database and displayed on the main calendar page.

I've successfully implemented algorithms for repeating events weekly, monthly by date, and yearly. However, I'm facing a challenge with monthly repetition based on weekdays. This refers to events that occur on the same weekday each month between the specified start and end dates.

For instance, an event might repeat on the first Monday of every month from March 1st to November 1st. The goal is to generate dates like April 5th (the first Monday in April) and continue this pattern until November.

The function below handles monthly repetition by date for events occurring on the 15th of any month:

function repeatEventMonthly(jsonArray, num){

// Extracting start and end dates from JSON and creating Date objects

var split = jsonArray[num].Fecha.split("/");
var split2 = jsonArray[num].fechaFin.split("/");

var dd = split[1];
var mm = split[0];
var yy = split[2];

var dd2 = split2[1];
var mm2 = split2[0];
var yy2 = split2[2];

var starDate = new Date();
var endDate = new Date();

starDate.setFullYear(yy);
starDate.setMonth(mm-1);
starDate.setDate(dd);
endDate.setFullYear(yy2);
endDate.setMonth(mm2-1);
endDate.setDate(dd2);

// Calculating days between start and end date

var top = getDaysInDates(starDate, endDate);

if (jsonArray[num].tipoRepeticion == "2") {

 // Handling Monthly by Weekday

}else if(jsonArray[num].tipoRepeticion == "3"){

    // Generating dates for Monthly by Date
    
    for (let index = 0; index < top; index++) {
        let sd = new Date(starDate);
        sd.setDate(sd.getDate()+index);
        if (sd.getDate() == starDate.getDate()) {
            let str = ((sd.getMonth()+1) + "/" + sd.getDate() + "/" + sd.getFullYear()).toString();
            eventMen.push({
                date: constructDates(str, 0, jsonArray[num].tipoRepeticion),
                title: jsonArray[num].titulo,
                descripcion: jsonArray[num].descripcion,
                tipo: jsonArray[num].tipo,
                tipoRepeticion : jsonArray[num].tipoRepeticion
            });
        }
    }
}

This function effectively generates events one month apart on the same date, such as repeating an event on the 3rd of each month between March and December. While I have tackled other types of recurring dates successfully, calculating monthly repetition by weekday poses a greater challenge due to varying month lengths. For example, determining the "first Monday of a month" requires more complex logic compared to fixed-date repetitions. Any suggestions or solutions on how to address this issue would be greatly appreciated. Additionally, there are various scenarios for monthly recurrence, not just limited to the "first Monday" but also involving the second Tuesday or last Friday of each month.

javascript json date

Answer 1

Answer №1

In order to retrieve the Nth occurrence of a specific day within a month, begin by setting a date for the first day of that month, then navigate to the first occurrence of the desired day and add (N-1) weeks' worth of days.

/* Function to obtain the Nth instance of a particular weekday in a month
 *
 * @param {number|string} nth - the Nth instance of the day (1 to 4)
 * @param {number|string} day - the day of the week (Sun 0, Mon 1, etc.)
 * @param {Date} month - any date within the target month
 * @returns {Date} representing the Nth instance of the specified day in the month
*/
function getNthDayInMonth(nth, day, month) {
  // Create a new date object for the 1st day of the month
  let d = new Date(month.getFullYear(), month.getMonth());
  // Move to the first instance of the day in the month and 
  // add (N - 1) weeks
  d.setDate(1 + (7 - d.getDay() + day)%7 + (nth - 1)*7);
  return d;
}

// Formatter
let f = (d) => new Intl.DateTimeFormat('en-GB', {
  weekday:'short',
  day:'2-digit',
  month:'short',
  year: 'numeric'
}).format(d);

// Examples
[[1,1,new Date(2021,11),'1st Mon in Dec 2021'],
 [3,3,new Date(2022, 0),'3rd Wed in Jan 2022'],
 [4,1,new Date(2022, 1),'4th Mon in Feb 2022'],
 [4,2,new Date(2022, 1),'4th Tue in Feb 2022'],
 [4,3,new Date(2022, 1),'4th Wed in Feb 2022'],
 [1,3,new Date(2022, 5),'1st Wed in Jun 2022'],
 [5,5,new Date(2022,11),'5th Fri in Dec 2022']
].forEach(a => {
  let [n,d,m,note] = a;
  console.log(`${note}: ${f(getNthDayInMonth(n,d,m))}`);
});

Each day in a month has at least 4 instances, with some having up to 5 occurrences (e.g. there are 5 Saturdays, Sundays, and Mondays in Jan 2022). The value of Nth may be restricted to 4, or extended to 5 only after ensuring it aligns with the end month being the same as the start month. If not, consider throwing an error or returning undefined.

To obtain all Nth days across months between two given dates, iterate through the months to extract the Nth instances, filtering out any dates falling before the start or beyond the end.

Answer 2

In order to retrieve the Nth occurrence of a specific day within a month, begin by setting a date for the first day of that month, then navigate to the first occurrence of the desired day and add (N-1) weeks' worth of days.

/* Function to obtain the Nth instance of a particular weekday in a month
 *
 * @param {number|string} nth - the Nth instance of the day (1 to 4)
 * @param {number|string} day - the day of the week (Sun 0, Mon 1, etc.)
 * @param {Date} month - any date within the target month
 * @returns {Date} representing the Nth instance of the specified day in the month
*/
function getNthDayInMonth(nth, day, month) {
  // Create a new date object for the 1st day of the month
  let d = new Date(month.getFullYear(), month.getMonth());
  // Move to the first instance of the day in the month and 
  // add (N - 1) weeks
  d.setDate(1 + (7 - d.getDay() + day)%7 + (nth - 1)*7);
  return d;
}

// Formatter
let f = (d) => new Intl.DateTimeFormat('en-GB', {
  weekday:'short',
  day:'2-digit',
  month:'short',
  year: 'numeric'
}).format(d);

// Examples
[[1,1,new Date(2021,11),'1st Mon in Dec 2021'],
 [3,3,new Date(2022, 0),'3rd Wed in Jan 2022'],
 [4,1,new Date(2022, 1),'4th Mon in Feb 2022'],
 [4,2,new Date(2022, 1),'4th Tue in Feb 2022'],
 [4,3,new Date(2022, 1),'4th Wed in Feb 2022'],
 [1,3,new Date(2022, 5),'1st Wed in Jun 2022'],
 [5,5,new Date(2022,11),'5th Fri in Dec 2022']
].forEach(a => {
  let [n,d,m,note] = a;
  console.log(`${note}: ${f(getNthDayInMonth(n,d,m))}`);
});

Each day in a month has at least 4 instances, with some having up to 5 occurrences (e.g. there are 5 Saturdays, Sundays, and Mondays in Jan 2022). The value of Nth may be restricted to 4, or extended to 5 only after ensuring it aligns with the end month being the same as the start month. If not, consider throwing an error or returning undefined.

To obtain all Nth days across months between two given dates, iterate through the months to extract the Nth instances, filtering out any dates falling before the start or beyond the end.

Answer 3

Answer №2

Find the day of the week for the first day of the month, then calculate the number of days until the desired day of the week. Proceed by adding multiples of 7 to reach the desired date.

For instance:

const startDate = new Date("2021-03-01"); // Mon Mar 01 2021
const friday = 5;        // Friday is the 5th day (Monday is 1)
const weekOfMonth = 2;   // Targeting the 3rd week (1st week is 0)

// Initiate calculations
const dayOfWeek = startDate.getUTCDay(); // 1
const diff = friday - dayOfWeek;         // 4
const dateOf3rdFriday = new Date(
    startDate.getUTCFullYear(),
    startDate.getUTCMonth(),
    startDate.getUTCDay() + diff + 7 * weekOfMonth
); // Fri Mar 19 2021

When aiming for the last Friday of the month, follow a similar approach in reverse.

Answer 4

Find the day of the week for the first day of the month, then calculate the number of days until the desired day of the week. Proceed by adding multiples of 7 to reach the desired date.

For instance:

const startDate = new Date("2021-03-01"); // Mon Mar 01 2021
const friday = 5;        // Friday is the 5th day (Monday is 1)
const weekOfMonth = 2;   // Targeting the 3rd week (1st week is 0)

// Initiate calculations
const dayOfWeek = startDate.getUTCDay(); // 1
const diff = friday - dayOfWeek;         // 4
const dateOf3rdFriday = new Date(
    startDate.getUTCFullYear(),
    startDate.getUTCMonth(),
    startDate.getUTCDay() + diff + 7 * weekOfMonth
); // Fri Mar 19 2021

When aiming for the last Friday of the month, follow a similar approach in reverse.

Answer 5

Answer №3

How to Find the nth Day of a Month Efficiently

Discover a unique approach that leverages a human-readable string while handling the 4th and 5th occurrences of a day within a month.

The user-friendly string format is exemplified as "1st Sun Dec" denoting a specific date.

If the final occurrence (the 5th instance) falls in the subsequent month, the second-to-last occurrence assumes the role of the last occurrence.

function nthDayInMonth(str , y) {
let days    = ["sun","mon","tue","wed","thu","fri","sat"],
    months  = ["jan","feb","mar","apr","may","jun","jul","aug","sep","oct","nov","dec"],
       pos  = ["1st","2nd","3rd","4th","last"],
[nth,day,m] = str.replace(/\s+/g," ").trim().toLowerCase().split(" ");
m  = months.indexOf(m);
let d = new Date(Date.UTC(y,m,1)),
    n = 1 + (7 - d.getDay() + days.indexOf(day))%7 + pos.indexOf(nth)*7;
d.setUTCDate(n);
return d.getUTCMonth()==m ? d : new Date(Date.UTC(y,m,n-7));
}
//================ tests ==========================
console.log(nthDayInMonth("1st Sun Dec",2023));  // 2023-12-03
console.log(nthDayInMonth("2nd Sun Dec",2023));  // 2023-12-10
console.log(nthDayInMonth("4th Sun Dec",2023));  // 2023-12-24
console.log(nthDayInMonth("last Sun Dec",2023)); // 2023-12-31
console.log(nthDayInMonth("Last   mon   dec",2023)); // 2023-12-25
console.log(nthDayInMonth("4th Sun Nov",2023));  // 2023-11-26 same as Last Sun Nov
console.log(nthDayInMonth("Last Sun Nov",2023)); // 2023-11-26 same as 4th Sun Nov

A Versatile Function to Identify the nth Day of a Month within a Date Range

The previous function can be slightly adapted to retrieve the nth Days of the Month within 2 provided dates.

This revised function yields an array containing the respective dates.

For instance, the following test cases showcase extracting the dates for the 1st Monday of each Month throughout 2023 and then identifying the dates for the last Friday of each Month during 2024.

function nthDayInMontBetweenDates(str,d1,d2) {
let days    = ["sun","mon","tue","wed","thu","fri","sat"],
       pos  = ["1st","2nd","3rd","4th","last"];
d1=new Date(d1); d2=new Date(d2);
let     m = d1.getUTCMonth(), arr=[],
[nth,day] = str.replace(/\s+/g," ").trim().toLowerCase().split(" ");
        y = d1.getFullYear();
while (d1<=d2) {
let d = new Date(d1),
    n = 1 + (7 - d.getDay() + days.indexOf(day))%7 + pos.indexOf(nth)*7;
    d.setUTCDate(n);
    arr.push(d.getUTCMonth()==m ? d : new Date(Date.UTC(y,m,n-7)));
    m++;
    m>11 && (m=0,y++);
    d1=new Date(Date.UTC(y,m,1));
}
return arr
}

console.log(nthDayInMontBetweenDates("1st Mon" ,"2023-01","2023-12"));
console.log(nthDayInMontBetweenDates("last fri","2024-01","2024-12"));

Answer 6

How to Find the nth Day of a Month Efficiently

Discover a unique approach that leverages a human-readable string while handling the 4th and 5th occurrences of a day within a month.

The user-friendly string format is exemplified as "1st Sun Dec" denoting a specific date.

If the final occurrence (the 5th instance) falls in the subsequent month, the second-to-last occurrence assumes the role of the last occurrence.

function nthDayInMonth(str , y) {
let days    = ["sun","mon","tue","wed","thu","fri","sat"],
    months  = ["jan","feb","mar","apr","may","jun","jul","aug","sep","oct","nov","dec"],
       pos  = ["1st","2nd","3rd","4th","last"],
[nth,day,m] = str.replace(/\s+/g," ").trim().toLowerCase().split(" ");
m  = months.indexOf(m);
let d = new Date(Date.UTC(y,m,1)),
    n = 1 + (7 - d.getDay() + days.indexOf(day))%7 + pos.indexOf(nth)*7;
d.setUTCDate(n);
return d.getUTCMonth()==m ? d : new Date(Date.UTC(y,m,n-7));
}
//================ tests ==========================
console.log(nthDayInMonth("1st Sun Dec",2023));  // 2023-12-03
console.log(nthDayInMonth("2nd Sun Dec",2023));  // 2023-12-10
console.log(nthDayInMonth("4th Sun Dec",2023));  // 2023-12-24
console.log(nthDayInMonth("last Sun Dec",2023)); // 2023-12-31
console.log(nthDayInMonth("Last   mon   dec",2023)); // 2023-12-25
console.log(nthDayInMonth("4th Sun Nov",2023));  // 2023-11-26 same as Last Sun Nov
console.log(nthDayInMonth("Last Sun Nov",2023)); // 2023-11-26 same as 4th Sun Nov

A Versatile Function to Identify the nth Day of a Month within a Date Range

The previous function can be slightly adapted to retrieve the nth Days of the Month within 2 provided dates.

This revised function yields an array containing the respective dates.

For instance, the following test cases showcase extracting the dates for the 1st Monday of each Month throughout 2023 and then identifying the dates for the last Friday of each Month during 2024.

function nthDayInMontBetweenDates(str,d1,d2) {
let days    = ["sun","mon","tue","wed","thu","fri","sat"],
       pos  = ["1st","2nd","3rd","4th","last"];
d1=new Date(d1); d2=new Date(d2);
let     m = d1.getUTCMonth(), arr=[],
[nth,day] = str.replace(/\s+/g," ").trim().toLowerCase().split(" ");
        y = d1.getFullYear();
while (d1<=d2) {
let d = new Date(d1),
    n = 1 + (7 - d.getDay() + days.indexOf(day))%7 + pos.indexOf(nth)*7;
    d.setUTCDate(n);
    arr.push(d.getUTCMonth()==m ? d : new Date(Date.UTC(y,m,n-7)));
    m++;
    m>11 && (m=0,y++);
    d1=new Date(Date.UTC(y,m,1));
}
return arr
}

console.log(nthDayInMontBetweenDates("1st Mon" ,"2023-01","2023-12"));
console.log(nthDayInMontBetweenDates("last fri","2024-01","2024-12"));

Is there a way to find the Nth occurrence of a specific weekday in each month between two given dates using JavaScript?

Answer №1

Answer №2

Answer №3

How to Find the nth Day of a Month Efficiently

A Versatile Function to Identify the nth Day of a Month within a Date Range

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