Fuzzy time from seconds.

fuzzytime.js

intervals = [
  {t: 0.001, s: 'a millisecond', p: '%d milliseconds'},
  {t: 1, s: 'a second', p: '%d seconds'},
  {t: 60, s: 'a minute', p: '%d minutes', m: 1},
  {t: 3600, s: 'an hour', p: '%d hours', m: 1},
  {t: 86400, s: 'a day', p: '%d days', m: 1},
  {t: 604800, s: 'a week', p: '%d weeks', m: 1},
  {t: 2629800, s: 'a month', p: '%d months', m: 2},
  {t: 31587840, s: 'a year', p: '%d years', m: 2},
];

function humanize(seconds, precise){
  const
    range = {start: 0, end: 0};
    parts = [];
  for (let i = 1, l = intervals.length; i < l && seconds / intervals[i].t >= 1; i++) {
    range.end = i;
  }
  if(!precise){
    range.start = range.end - (intervals[range.end].m || 0);
  }
  for (let i = range.end, l = range.start - 1; i > l && seconds; i--) {
    const
      interval = intervals[i],
      part = parseInt(seconds / interval.t);
    if(part > 0){
      seconds = Math.max(0, seconds - part * interval.t);
      parts.push(part == 1 ? interval.s.replace('%d', part) : interval.p.replace('%d', part));
    }
  }
  return parts[1] ? [parts.pop(), parts.join(', ')].reverse().join(' and ') : parts[0];
}

console.log('Fuzzy:', humanize(1000000000));
console.log('Precise:', humanize(1000000000, true));
console.log('Fuzzy:' ,humanize(10000000));
console.log('Precise:', humanize(10000000, true));
console.log('Fuzzy:', humanize(1000000));
console.log('Precise:', humanize(1000000, true));
console.log('Fuzzy:', humanize(100000));
console.log('Precise:', humanize(100000, true));
console.log('Fuzzy:', humanize(10000));
console.log('Precise:', humanize(10000, true));
console.log('Fuzzy:', humanize(1000));
console.log('Precise:', humanize(1000, true));
console.log('Fuzzy:', humanize(100.25));
console.log('Precise:', humanize(100.25, true));
console.log('Fuzzy:', humanize(10.25));
console.log('Precise:', humanize(10.25, true));
console.log('Fuzzy:', humanize(0.25));
console.log('Precise:', humanize(0.25, true));

/*
Fuzzy: 31 years, 7 months and 3 weeks
Precise: 31 years, 7 months, 3 weeks, 6 days, 9 hours, 52 minutes and 40 seconds
Fuzzy: 3 months, 3 weeks and 3 days
Precise: 3 months, 3 weeks, 3 days, 10 hours, 16 minutes and 40 seconds
Fuzzy: a week and 4 days
Precise: a week, 4 days, 13 hours, 46 minutes and 40 seconds
Fuzzy: a day and 3 hours
Precise: a day, 3 hours, 46 minutes and 40 seconds
Fuzzy: 2 hours and 46 minutes
Precise: 2 hours, 46 minutes and 40 seconds
Fuzzy: 16 minutes and 40 seconds
Precise: 16 minutes and 40 seconds
Fuzzy: a minute and 40 seconds
Precise: a minute, 40 seconds and 250 milliseconds
Fuzzy: 10 seconds
Precise: 10 seconds and 250 milliseconds
Fuzzy: 250 milliseconds
Precise: 250 milliseconds
*/