const getNextMonth = (startDate) => {

  let current;

  if (startDate.getMonth() == 11) {

    current = new Date(startDate.getFullYear() + 1, 0, 1);

  } else {

    current = new Date(startDate.getFullYear(), startDate.getMonth() + 1, 1);

  }

​

  return current.getMonth();

};

​

let startDate = new Date();

getNextMonth(startDate);

const outputDate = (date, output = 'month') => {

  switch (output) {

    default:

    case 'month':

      return date.getMonth();

    case 'fulldate':

      return date;

    case 'year':

      return date.getFullYear();

  }

};

​

const changeMonth = (current = new Date(), change) => {

  if (change === 0) return current;

​

  const unformatted = new Date(current).setMonth(current.getMonth() + change);

  const formatted = new Date(unformatted);

  return formatted;

};

​

const getNextMonth = (current = new Date(), output = 'month') => {

  const nextMonth = changeMonth(current, 1);

  return outputDate(nextMonth, output);

};

​

let startDate = new Date();

getNextMonth(startDate)

const changeMonth = (current, change) => {

  if (change === 0) return current;

​

  const unformatted = new Date(current).setMonth(current.getMonth() + change);

  return new Date(unformatted);

};

​

const getNextMonth = (current) => {

  return changeMonth(current, 1).getMonth()

};

​

let startDate = new Date();

getNextMonth(startDate)

const getNextMonth = (current) => {

  const unformatted = new Date(current).setMonth(current.getMonth() + 1)

  return new Date(unformatted).getMonth()

};

​

let startDate = new Date();

getNextMonth(startDate)