formatDuration.js

// noprotect
console.clear();

const second = 1;
const minute = second * 60;
const hour = minute * 60;
const day = hour * 24;
const year = day * 365;

const unitValues = [{
  unit: 'year',
  value: year
}, {
  unit: 'day',
  value: day
}, {
  unit: 'hour',
  value: hour
}, {
  unit: 'minute',
  value: minute
}, {
  unit: 'second',
  value: second
}];

function formatDuration(inputSecs) {
  if (typeof inputSecs !== 'number' || inputSecs < 0 || isNaN(inputSecs)) {
    throw new TypeError('formatDuration() may only be called with a non-negative number');
  }

  if (inputSecs === 0) {
    return 'now';
  }

  const parts = [];
  let secsRemaining = inputSecs;
  
  for (const { unit, value } of unitValues) {
    const count = Math.floor(secsRemaining / value);

    if (count > 0) {
      secsRemaining -= count * value;
      const label = count > 1 ? unit + 's' : unit;
      parts.push(`${count} ${label}`);
    }
  }

  if (parts.length === 1) {
    return parts[0];
  }
  
  const last = parts.pop();
  
  return `${parts.join(', ')} and ${last}`;
}