AngularJS directive using bootstrap-multiselect that written in Coffeescript and with underscore.js

angular-bootstrap-multiselect.coffee

angular.module('appModule')
  .directive 'appDirective', ->

    ($scope, elem, attr) ->

      elem.multiselect
        buttonClass : 'btn btn-small'
        buttonWidth : '200px'
        buttonContainer : '<div class="btn-group" />'
        maxHeight : 200
        includeSelectAllOption: true
        buttonText: (options) ->
          if options.length is 0
            return elem.data()['placeholder'] + ' <b class="caret"></b>'
          else if options.length > 1
            return _.first(options).text + ' + ' + (options.length - 1) + ' more selected <b class="caret"></b>'
          else
            return _.first(options).text + ' <b class="caret"></b>'

        # Replicate the native functionality on the elements so
        # that angular can handle the changes for us.
        onChange: (optionElement, checked) ->
          optionElement.removeAttr('selected')
          if checked
            optionElement.attr('selected', 'selected')
          elem.change()

      # Watch for any changes to the length of our select element
      $scope.$watch () ->
        return elem[0].length
      , () ->
        elem.multiselect('rebuild')
      
      # Watch for any changes from outside the directive and refresh
      $scope.$watch(attr.ngModel, () ->
        elem.multiselect('refresh'))