Simple AngularJS directive for drag and drop file upload in coffeescript

dropzone.coffee

angular
    .module 'DropzoneDirective', []
    .directive 'dropzone', ->
        restrict: 'A'
        scope :
            onComplete : '&'
        link: (scope, element, attrs) ->
            element.bind 'dragover', (event) ->
                event.stopPropagation()
                event.preventDefault()
                element.addClass 'state-hover'

                return

            element.bind 'drop', (event) ->
                event.stopPropagation()
                event.preventDefault()
                
                element.removeClass 'state-hover'

                files = event.dataTransfer.files
                reader = new FileReader()

                reader.onload = (event) ->
                    data = btoa event.target.result
                    scope.onComplete file : data

                    return

                reader.readAsText(files[0], 'UTF-8')

                return

            element.bind 'dragleave', (event) ->
                event.stopPropagation()
                event.preventDefault
                element.removeClass 'state-hover'

                return

            return