relative_time.js

function relativeTime(date) {
  var units = {
    year: 31557600000,
    month: 2629800000,
    week: 604800000,
    day: 86400000,
    hour: 3600000,
    minute: 60000,
    second: 1000
  };

  var delta = new Date() - new Date(date);

  for (var unit in units) {
    if (units.hasOwnProperty(unit)) {
      if (delta >= units[unit]) {
        var time = Math.floor(delta / units[unit]);
        var unitName = unit + (time > 1 ? 's' : '');
        return [time, unitName, 'ago'].join(' ');
      }
    }
  }

  return 'Now';
}