Ember plugin: Extensible className additions http://discuss.emberjs.com/t/extensible-classname-additions/9601

ember.classy.js

import Ember from 'ember'

const pushTo = key => ( ...items ) =>
  Ember.Mixin.create( {
    init(){
      this._super( ...arguments )

      this[ key ].push( ...items )
    }
  } )

const names    = pushTo( 'classNames' )
const bindings = pushTo( 'classNameBindings' )

export default Object.assign( names, { names, bindings } )