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JavaScript

/**
     * Returns count of weeks for year and month
     *
     * @param {Number} year - full year (2016)
     * @param {Number} month_number - month_number is in the range 1..12
     * @returns {number}
     */
var weeksCount = function(year, month_number) {
  var firstOfMonth = new Date(year, month_number - 1, 1);
  var day = firstOfMonth.getDay() || 6;
  day = day === 1 ? 0 : day;
  if (day) { day-- }
  var diff = 7 - day;
  var lastOfMonth = new Date(year, month_number, 0);
  var lastDate = lastOfMonth.getDate();
  if (lastOfMonth.getDay() === 1) {
  	diff--;
  }
  var result = Math.ceil((lastDate - diff) / 7);
  return result + 1;
};
console.log(weeksCount(2016, 10));