Relative date

relative-date.js

function relativeDate(str) {
  var s = (+new Date() - Date.parse(str)) / 1e3,
      m = s / 60,
      h = m / 60,
      d = h / 24,
      w = d / 7,
      y = d / 365.242199,
      M = y * 12,
      R = Math.round;
  return s <= 5 ? 'just now'
       : m < 1  ? R(s) + ' seconds ago'
       
       : R(m) <= 1 ? 'a minute ago'
       : h < 1  ? R(m) + ' minutes ago'
       
       : R(h) <= 1 ? 'an hour ago'
       : d < 1  ? R(h) + ' hours ago'
       
       : R(d) <= 1 ? 'yesterday'
       : w < 1  ? R(d) + ' days ago'
       
       : R(w) <= 1 ? 'a week ago'
       : M < 1  ? R(w) + ' weeks ago'
       
       : R(M) <= 1 ? 'a month ago'
       : y < 1  ? R(M) + ' months ago'
       
       : R(y) <= 1 ? 'a year ago'
       : R(y) + ' years ago';
};

Just rewrote the whole thing, inspired by (and heavily based on) @cowboy’s fork of this gist. Thanks Ben!