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In a NodeJS game with each object as a class, how should events be handled?

When you work with several classes in a Javascript / NodeJS game, it’s hard for me to understand which class should emit events and which classes should listen. I follow this guide to creating event-driven games: http://pragprog.com/magazines/2011-08/decouple-your-apps-with-eventdriven-coffeescript

I am writing a small game and divided my classes into the following controllers:

world - creates a game world and develops through several "turns" to determine some simple logic of the game (i.e., the character must move, the tower must shoot).

tower - the tower sits on a 10x10 grid and has a range. When an object falls within range, it can shoot.

mobs (enemies) - the crowd appears on a 10x10 grid and moves every 3 seconds. At some point, he wanders within the tower.

I read about EventEmitters all day, but can't figure out how to properly build my events. Should mobs shoot an event when they move and the tower listens to the "move" event? Or should the world control all the events, and the tower / mobs are listening to the world?

See below for sample code.

Reference Information. I was working on a simple TowerD game for NodeJS and decided to implement the server first. I store all the objects in MongoDB and using geospatial analysis to determine if the objects are in range for shooting. I am currently using a rudimentary 3-second loop to “tick off” the game logic and progress, but I would like to move on to a truly event-driven model and am afraid.

:

exports.World = class World extends EventEmitter

  constructor: ->
    ### Initial config ###
    @gameTime = 3000  # every 3000ms, the game progresses

    ### Start the game!! ###
    @game = setInterval ->
      world.gameLoop()
    , @gameTime

    ### Load the map ###
    # First level: Hidden Valley
    @maps = []
    @maps.push new map 'hiddenvalley'

### Load the mobs ###
    # First map has one mob: Warrior
    @mobs = []

    # Let create two of them  
    @mobs.push new mob @maps[0].mobs[0]
    @mobs.push new mob @maps[0].mobs[0]

(. world.coffee: https://github.com/bdickason/node-towerd/blob/master/controllers/world.coffee)

:

exports.Tower = class Tower
  constructor: (name) ->
    name = name.toLowerCase() # In case someone throws in some weird name

  # Check for anything within range
  checkTargets: (callback) ->
    mobModel.find { loc : { $near : @loc , $maxDistance : @range } }, (err, hits) -> 
      if err
        console.log 'Error: ' + err
      else
        callback hits

(. towers.coffee: https://github.com/bdickason/node-towerd/blob/master/controllers/towers.coffee)

:

exports.Mob = class Mob extends EventEmitter

  move: (X, Y, callback) ->
    @loc = [@loc[0] + X, @loc[1] + Y]
    newloc = @loc
    mobModel.find { uid: @uid }, (err, mob) ->
      if(err)
        console.log 'Error finding mob: {@uid} ' + err
      else
        mob[0].loc = newloc
        mob[0].save (err) ->
          if (err)
            console.log 'Error saving mob: {@uid} ' + err
    console.log 'MOB ' + @uid + ' [' + @id + '] moved to (' + @loc[0] + ',' + @loc[1] + ')'

(. mobs.coffee: https://github.com/bdickason/node-towerd/blob/master/controllers/mobs.coffee)

: https://github.com/bdickason/node-towerd

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