Convert milliseconds to readable format

const formatDuration = ms => {
  if (ms < 0) ms = -ms;
  const time = {
    day: Math.floor(ms / 86400000),
    hour: Math.floor(ms / 3600000) % 24,
    minute: Math.floor(ms / 60000) % 60,
    second: Math.floor(ms / 1000) % 60,
    millisecond: Math.floor(ms) % 1000
  };
  return Object.entries(time)
    .filter(val => val[1] !== 0)
    .map(([key, val]) => `${val} ${key}${val !== 1 ? 's' : ''}`)
    .join(', ');
};

How it works

This function takes an argument of milliseconds and returns a readable format using days, hours, minutes, seconds, and milliseconds. For example, passing in 34325055574 would return '397 days, 6 hours, 44 minutes, 15 seconds, 574 milliseconds'.

This function pairs well with the JavaScript code snippet for calculating the difference between two dates.

Source: Format duration and licensed under CC BY 4.0