a way to reflect keyboard state as a backbone model.

keyboard.coffee

define [
  'zepto',
  'backbone'
], ($, Backbone) ->
  
  # a singleton backbone.model whose
  # attributes represent keyboard state
  new class extends Backbone.Model
    
    # bind keyboard events to model state
    initialize: ->
      
      # maps keyCode to property name
      key = (w) =>
        switch w
          when 38 then 'up'
          # etc...

      # returns an event handler who
      # sets state based on val and keyCode
      set = (val) =>
        (e) => @set key(e.which), val

      # bind keyup/keydown to model
      # property values
      $ =>
        $doc = $(document)
        $doc.bind 'keyup', set(false)
        $doc.bind 'keydown', set(true)

      Backbone.Model::initialize.apply @, arguments