Print next "n" week after a given date in JavaScript

nextNWeekAfterDate.js

// Three-letter abbreviations of months
const monthAbbrev = 'Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec'.split(' ');
// One day in milliseconds. Used for creating new dates "x" days after a given date
const dayMs = 24 * 60 * 60 * 1000;
// I could have just used toLocaleDateString, but this is more flexible and easier to adjust to your needs
const formatDateSimple = d => `${d.getFullYear()} ${monthAbbrev[d.getMonth()]} ${d.getDate()}`;

function getWeekStr(startDate, weekCount, formatDate) {
  const weekRange = new Array(weekCount);
  for (let i = 0; i < weekCount; i += 1) {
    const starts = new Date(startDate.getTime() + i * 7 * dayMs);
    const ends = new Date(startDate.getTime() + 6 * dayMs + i * 7 * dayMs);
    weekRange[i] = `${formatDate(starts, i)} - ${formatDate(ends, i)}`;
  }
  return weekRange.join('\n');
}

getWeekStr(new Date(2018, 0, 15), 12, formatDateSimple);

/* // Example string return value:
2018 Jan 15 - 2018 Jan 21
2018 Jan 22 - 2018 Jan 28
2018 Jan 29 - 2018 Feb 4
2018 Feb 5 - 2018 Feb 11
2018 Feb 12 - 2018 Feb 18
2018 Feb 19 - 2018 Feb 25
2018 Feb 26 - 2018 Mar 4
2018 Mar 5 - 2018 Mar 11
2018 Mar 12 - 2018 Mar 18
2018 Mar 19 - 2018 Mar 25
2018 Mar 26 - 2018 Apr 1
2018 Apr 2 - 2018 Apr 8
*/