mixins

gistfile1.js

var emptyFunction = () => {}

/**
 * creates a new constructor function with `objects` merged in its prototype.
 * to prevent unwanted errors when calling `super()` a child class, the
 * prototype is actually a proxy returning **or** the actual method, or an
 * empty function.
 *
 * as the proxy gets the same shape as the initial object, the prototype chain
 * actually receives the present methods.
 *
 * @param {Object} ...objects
 * @returns {Function}
 */
function mixins(...objects) {
  var proto = {}
  objects.forEach((object) => {
    if(object == null || object === false) {
      return
    }
    for(let methodName in object) {
      let previousMethod = proto[methodName]
      let method = object[methodName]
      let actualMethod = method
      if(previousMethod) {
        // if mixins have multiple methods, we merge them
      	actualMethod = function(...args){
       	  previousMethod.apply(this, args)
       	  method.apply(this, args)
        }
      }
      proto[methodName] = actualMethod
    }
  })
  function ComposedClass(){
    ComposedClass.prototype.constructor.apply(this, arguments)
  }
  ComposedClass.prototype = new Proxy(proto, {
    get(object, methodName) {
      return proto[methodName] || emptyFunction
    },
    set() {
      throw new TypeError()
    }
  })
  return ComposedClass
}

const A = {
  constructor() {
    this.name = "defaultName"
  },
  getName() {
    return this.name
  },
  setName(name) {
    this.name = name
  }
}

const B = {
  constructor() {
    this.foo = "bar"
  }
}

class Test extends mixins(A, B) {
  constructor() {
    super()
  }
  test() {
    super() // doesn't throw, as the proxy returns an empty function
    return "foo"
  }
}

const t = new Test()

console.log(t.name)
console.log(t.foo)
console.log(t.test())

a little idea with mixins implementing the class mixin idea from @sebmarkbage with
the help of ES6 proxies to prevent super() to throw if no method in the prototype chain is matching
this call.