How many days of the week do you have in the month? [closed]

closed. this question is out of scope and is not currently accepting answers.

want to improve this question? Update the question so it's on-topic for Stack Overflow.

Closed 6 months ago .

improve this question

Hello, good night!

I did a lot of research on the internet and found nothing concerning this doubt! I would like to get how many days of the week there is within a month using javascript! Example: 

Quantos sábados existe no mês de atual? = 5
Quantas terças-feiras existes no mês atual? = 4

I would like a script where it would tell me the number of days that exists in the current month.

Thank you right now...

Author: Guilherme Nunes, 2020-08-05
Source

2 answers

I made a library to generate dates, Week number etc that I use in my projects, can be useful to you.

In this case it's simple and you can do it in JavaScript. Note that this script is insensitive to holidays :), you have to add this logic by hand.

function getWorkingDays(month) {
  const date = new Date(2020, month, 1, 0, 0, 0);
  let workingdays = 0;
  while (month === date.getMonth()) {
    const currentDay = date.getDay();
    const isWeekend = (currentDay === 6) || (currentDay === 0);
    if (!isWeekend) workingdays++; // se não é fds aumentar o nr
    date.setDate(date.getDate() + 1); // testar o próximo dia
  }
  return workingdays;
}

// lembra-te que meses têm base 0
// ou seja: janeiro é o mes 0, fevereiro o mes 1, etc...

console.log(getWorkingDays(0));
console.log(getWorkingDays(1));

To know the number of specific days you can make an adaptation of the Code: 

function getDaysByType(month, type) {
  const date = new Date(2020, month, 1, 0, 0, 0);
  let count = 0;
  while (month === date.getMonth()) {
    if (date.getDay() === type) count++;
    date.setDate(date.getDate() + 1); // testar o próximo dia
  }
  return count;
}

// sábado tem o nr 6
// domingo tem o nr 0
// segunda tem o nr 1
// etc

console.log(getDaysByType(0, 0));
console.log(getDaysByType(0, 1));
console.log(getDaysByType(0, 2));
console.log(getDaysByType(0, 3));
console.log(getDaysByType(0, 4));
console.log(getDaysByType(0, 5));
console.log(getDaysByType(0, 6));
 4
Author: Sergio, 2020-08-05 05:43:44

Using a while summing days until solves the problem: 

 while (month === date.getMonth()) {
   if (date.getDay() === type) count++;
   date.setDate(date.getDate() + 1); // testar o próximo dia
 }

But the increment of date.getDate() + 1 will generate increments and on average 30 loops , most of which are unnecessary, if the required rule is a specific day of the Week just add +7 inside the loop instead of +1 and check if it is the same month later and then yes do the sum count++, the function a little optimized can be like this (as the test done at the end of the answer was almost 3 times more Fast): 

function getDaysByType(type, month, year) {
  const date = new Date(year ? year : new Date().getFullYear(), month, 1, 0, 0, 0);

  var count = 0, increment = 1;

  while (month === date.getMonth()) {
    if (date.getDay() === type) {
        count++;
        increment = 7;
    }

    date.setDate(date.getDate() + increment); // testar o próximo dia
  }
  return count;
}

console.log('Quantidade de Sábados em Janeiro:', getDaysByType(0, 0));
console.log('Quantidade de Sábados em Fevereiro:', getDaysByType(0, 1));
console.log('Quantidade de Sábados em Março:', getDaysByType(0, 2));
console.log('Quantidade de Sábados em Abril:', getDaysByType(0, 3));
console.log('Quantidade de Sábados em Maio:', getDaysByType(0, 4));
console.log('Quantidade de Sábados em Junho:', getDaysByType(0, 5));
console.log('Quantidade de Sábados em Julho:', getDaysByType(0, 6));

This way will be 4-11 loops instead of 28-31 loops, which made ~70% faster.

However I have another proposal, use the basic math, because if we know that a day of the week can appear between 4 and 5 times in the same month with this we already have how to get by a calculation, we will only need to know which the first day of the week of a month and which]}

This way got ~90% faster :

Remembering that 0 = Saturday, 1 = Sunday, 2 = Monday, 3 = Tuesday, 4 = Wednesday, 5 = Thursday, 6 = Friday

Month from 0 (January) to 11 (December) 

function sumWeekDaysInMonth(weekday, month, year)
{
    if (!year) year = new Date().getFullYear();

    // Obtem o ultimo dia do mês
    var daysInMonth = new Date(year, month + 1, 0).getDate();

    // Obtem primeiro dia da semana do mês
    var firstWeekDay = new Date(year, month, 1).getDay();

    return Math.floor((daysInMonth + (weekday + firstWeekDay) % 7) / 7);
}

console.log('Quantidade de Sábados em Janeiro (ano atual):', sumWeekDaysInMonth(6, 0));
console.log('Quantidade de Sábados em Fevereiro (ano atual):', sumWeekDaysInMonth(6, 1));
console.log('Quantidade de Sábados em Março (ano atual):', sumWeekDaysInMonth(6, 2));

console.log('----');

console.log('Quantidade de Sábados em Janeiro 1988:', sumWeekDaysInMonth(6, 0, 1988));
console.log('Quantidade de Sábados em Fevereiro 1988:', sumWeekDaysInMonth(6, 1, 1988));
console.log('Quantidade de Sábados em Março 1988:', sumWeekDaysInMonth(6, 2, 1988));

To better understand, we use % to get what's left in a division, SO:

Day of the week + first day of the week of the month / total days Week (7)

In January was (6 + 3) % 7 = 2 (it would be like 6+3=9 and 9/7=1,2, rounding gets 2)

Then add the number of days in the month and divide by 7, 4 was the remaining result of the Division:

(31 + 2) / 7 = 4,714285714285714

Then uses Math.floor() to return the smallest integer that will be " 4 " for the month of January 2020

See the benchmark for All codes: https://jsbench.me/lwkdh223r9/1

benchmark result

  • With optimized while managed to run almost 3 times faster

  • With "math" was the faster performing almost 10 times faster

 8
Author: Guilherme Nascimento, 2020-08-05 21:51:16