Auto-update collection changes in backbone

dogCollection.coffee

class sp.collections.DogCollection extends Backbone.Collection

  initialize: ->
    @fetch()
    setInterval(@fetchChanges, 15*1000)

  model: sp.models.DogModel
  
  url: '/dogs'

  changesUrl: ->
    u = @url
    if @length > 0 then u += "?lastUpdated="+@lastUpdated()
    u
    
  fetchChanges: =>
    @fetch({add:true, merge:true, url: @changesUrl()})

  lastUpdated: ->
    lastModelUpdated = @max (model) ->
      new Date(model.get('lastUpdated'))
    lastModelUpdated.get('lastUpdated')