Rails helper time_ago_in_words() and distance_of_time_in_words() translated into coffee script. Check out http://apidock.com/rails/ActionView/Helpers/DateHelper/distance_of_time_in_words for the rails documentation.

time.js.coffee

time_ago_in_words = (from_time, include_seconds) ->
  include_seconds ?= false
  App.distance_of_time_in_words(from_time, Date.now(), include_seconds)

distance_of_time_in_words = (from_time, to_time, include_seconds) ->
  include_seconds ?= false
  to_time ?= 0

  distance_in_minutes = Math.round(Math.abs(to_time - from_time) / 60 / 1000)
  distance_in_seconds = Math.round(Math.abs(to_time - from_time) / 1000)
  
  if 0 <= distance_in_minutes && distance_in_minutes <= 1
    unless include_seconds
      if distance_in_minutes == 0
        return "less than 1 minute ago"
      else
        return "#{distance_in_minutes} minutes ago"
    if 0 <= distance_in_seconds && distance_in_seconds <= 4  
      "less than 5 seconds ago"
    else if 5 <= distance_in_seconds && distance_in_seconds <= 9  
      "less than 10 seconds ago"
    else if 10 <= distance_in_seconds && distance_in_seconds <= 19  
      "less than 20 seconds ago"
    else if 20 <= distance_in_seconds && distance_in_seconds <= 39  
      "less than half a minute ago"
    else if 40 <= distance_in_seconds && distance_in_seconds <= 59 
      "less than 1 minute ago"
    else "1 minute ago"

  else if 2 <= distance_in_minutes && distance_in_minutes <= 44
    "#{distance_in_minutes} minutes ago"
  else if 45 <= distance_in_minutes && distance_in_minutes <= 89  
    "about 1 hour ago"
  else if 90 <= distance_in_minutes && distance_in_minutes <= 1439
    "about #{Math.round(distance_in_minutes/60.0)} hours ago"
  else if 1440 <= distance_in_minutes && distance_in_minutes <= 2529
    "1 day ago"
  else if 2530 <= distance_in_minutes && distance_in_minutes <= 43199
    "#{Math.round(distance_in_minutes/1440.0)} days ago"
  else if 43200 <= distance_in_minutes && distance_in_minutes <= 86399
    "about 1 month ago"
  else if 86400 <= distance_in_minutes && distance_in_minutes <= 525599
    "#{Math.round(distance_in_minutes/43200.0)} months ago"
  else
    distance_in_years = distance_in_minutes / 525600
    minute_offset_for_leap_year = (distance_in_years/4) * 1440
    remainder = ((distance_in_minutes - minute_offset_for_leap_year) % 525600)
    if remainder < 131400
      "about #{Math.round(distance_in_years)} years ago"
    else if remainder < 394200
      "over #{Math.round(distance_in_years)} years ago"
    else
      "almost #{Math.round(distance_in_years+1)} years ago"