Solution for http://www.codewars.com/dojo/katas/52742f58faf5485cae000b9a

formatDuration.js

function formatDuration (seconds) {
  // Complete this function
  if (seconds === 0) return 'now';
  
  var calc = {
      years: {time: 60*60*24*365, str: 'year'},
      days: {time: 60*60*24, str: 'day'},      
      hours: {time: 60*60, str: 'hour'},
      mins: {time: 60, str: 'minute'}
    }, duration = [];
  
  for (var c in calc) {
    var time = Math.floor(seconds / calc[c].time);     
    if (time > 0 && time !== calc[c].time) {
      seconds -= time*calc[c].time;
      duration.push(time + ' ' + calc[c].str + ((time > 1) ? 's' : ''));
    }
  }  
  if (seconds > 0) { duration.push(seconds + ' ' + 'second' + ((seconds > 1) ? 's' : '')); }
  
  return duration.join(', ').replace(/,\s$/, '').replace(/,\s([^,]+)$/, ' and $1');  
}