Get the difference between dates in a human readable format (like "2 years, 3 months").

get-duration.js

// Both params accept the same format as the Date object (IETF-compliant RFC 2822 timestamps and also a version of ISO8601).
// This is a basic version (supports just years and months, it assumes every month is 30 days, no pluralization, etc.) but it works.
const getDuration = (startDateString, endDateString = new Date()) => {
  const totalMonths = Math.floor((new Date(endDateString) - new Date(startDateString)) / 1000 / 60 / 60 / 24 / 30);
  const months = totalMonths < 12 ? totalMonths : totalMonths % 12;
  const years = Math.floor(totalMonths / 12);
  let duration = '¯\_(ツ)_/¯';

  if (years === 0)
    if (months > 0)
      duration = `${months} months`;
  if (years > 0)
    if (months === 0)
      duration = `${years} years`;
    else
      duration = `${years} years, ${months} months`;

  return `${duration}`;
};