Extend the idea from http://blog.yorkxin.org/posts/2014/06/10/mixin-and-concern-in-javascript

concerning.coffee

#=require underscore.js

class BaseClass
  @concerning: (concernName, concernObj) ->
    functionsToCopy = _.omit(mixin, "included", "classFunctions")
    _.extend(this.prototype, functionsToCopy)
    _.extend(this, concernObj.classFunctions)

    if typeof concernObj.included is "function"
      concernObj.included.call(concernObj, this)

Duck = 
  quake: -> "Quake!"

class Kamo extends BaseClass
  @act: -> console.log "Acted"

  @concerning "Sound", {
    included: (base) ->
      do base.act

    quake: -> console.log "Quake!"
  }