When the first week of the year begins. ISO8601. JavaScript

[Juan_Antonio]

The ISO 8601 definition for week 01 is the week with the first Thursday of the Gregorian year
If 1 January is on a Monday, Tuesday, Wednesday or Thursday, it is in W01. If it is on a Friday, it is part of W53 of the previous year. If it is on a Saturday, it is part of the last week of the previous year which is numbered W52 in a common year and W53 in a leap year. If it is on a Sunday, it is part of W52 of the previous year.

https://en.wikipedia.org/wiki/ISO_week_date

What is the first day of the week?

• We are going to create an app that shows us the days of the first week of each year, for this we are going to use ChatGPT, we will ask:
  
  

(Adapted to App Inventor)

semana.htm

<script>
function getWeekDays(year, week) {
  const startDate = getWeekStartDate(year, week);
  const weekDays = [];

  for (let i = 0; i < 7; i++) {
    const currentDate = new Date(startDate);
    currentDate.setDate(startDate.getDate() + i);
    weekDays.push(currentDate.toDateString());
  }

  return weekDays;
}

function getWeekStartDate(year, week) {
  const jan1 = new Date(year, 0, 1);
  const jan1DayOfWeek = jan1.getDay();
  let startDate;

  if (jan1DayOfWeek <= 4) {
    startDate = new Date(year, 0, 1 - jan1DayOfWeek + 1);
  } else {
    startDate = new Date(year, 0, 1 + (7 - jan1DayOfWeek) + 1);
  }

  startDate.setDate(startDate.getDate() + (week - 1) * 7);

  return startDate;
}


datos =  window.AppInventor.getWebViewString().split(","); // Entrada de datos.
var year = datos[0];
var week = datos[1];
const weekDays = getWeekDays(year, week);

weekDays.forEach(day => console.log(day));
const weekDaysJSON = JSON.stringify(weekDays);
 window.AppInventor.setWebViewString("" + weekDaysJSON);  
</script>

p100_Semana_JS.aia (3.9 KB)

[Juan_Antonio]

2.- Day of the week of 31 December.

From: https://en.wikipedia.org/wiki/ISO_week_date

Did you know... these symbols mean floor and ceil?

p100_Semana_JS_v2.aia (4.5 KB)

• Remember that in the ISO8601 standard the weeks start on Monday.

[elmachi130]

@Juan_Antonio

App

consulta
como puedo calcular o obtener la cantidad de semanas de un año
como por ejemplo
2023 tiene 52
2020 tiene 53

saludos

[TIMAI2]

@elmachi130

how can I calculate or get the amount of weeks in a year

I showed you in your topic....

[Juan_Antonio]

3.- Number of weeks in a year according to ISO8601.

p100_Semana_JS_v3.aia (5.3 KB)

Label2 is last day of the year. (1: Monday - ........... - 0: Sunday)

[Juan_Antonio]

4.- Format date: DD MM YYYY

semana.htm

<script>
function getWeekDays(year, week) {
  const startDate = getWeekStartDate(year, week);
  const weekDays = [];

for (let i = 0; i < 7; i++) {
    const currentDate = new Date(startDate);
    currentDate.setDate(startDate.getDate() + i);
    const formattedDate = formatDate(currentDate);
    weekDays.push(formattedDate);
  }

  return weekDays;
}

function formatDate(date) {
  const day = String(date.getDate()).padStart(2, '0');
  const month = String(date.getMonth() + 1).padStart(2, '0');
  const year = date.getFullYear();
  return `${day} ${month} ${year}`;
}

function getWeekStartDate(year, week) {
  const jan1 = new Date(year, 0, 1);
  const jan1DayOfWeek = jan1.getDay();
  let startDate;

  if (jan1DayOfWeek <= 4) {
    startDate = new Date(year, 0, 1 - jan1DayOfWeek + 1);
  } else {
    startDate = new Date(year, 0, 1 + (7 - jan1DayOfWeek) + 1);
  }

  startDate.setDate(startDate.getDate() + (week - 1) * 7);

  return startDate;
}


datos =  window.AppInventor.getWebViewString().split(","); // Entrada de datos.
var year = datos[0];
var week = datos[1];
const weekDays = getWeekDays(year, week);

weekDays.forEach(day => console.log(day));
const weekDaysJSON = JSON.stringify(weekDays);
 window.AppInventor.setWebViewString("" + weekDaysJSON);  
</script>