Find week number using vanillaJs.

getWeekNumber.js

/**
 * Calculates the week number of a given date.
 * @param {Date} date - The date for which to calculate the week number.
 * @returns {number} - The week number of the provided date.
 */
function getWeekNumber(date) {
  const dd = date.getDate();
  const mm = date.getMonth();
  const yyyy = date.getFullYear();
  
  // Get the index of the first day of the month
  const firstDayIndex = new Date(yyyy, mm, 1).getDay();
  
  // Calculate the week number
  const weekNumber = Math.floor(firstDayIndex + dd / 7);
  
  return weekNumber;
}