Maybe you can try to update the code with Reflect?

[rxliuli]

Just think that ES6 is not trying to use Reflect?

Modified the code

var aggregation = (base, ...mixins) => {
  /*  create aggregation class  */
  let aggregate = class __Aggregate extends base {
    constructor (...args) {
      /*  call base class constructor  */
      super(...args)

      /*  call mixin's initializer  */
      mixins.forEach(mixin => {
        if (typeof mixin.prototype.initializer === 'function') { mixin.prototype.initializer.apply(this, args) }
      })
    }
  }

  /*  copy properties  */
  let copyProps = (target, source) => {
    Reflect.ownKeys(source)
      .forEach(prop => {
        if (
          prop.match(
            /^(?:initializer|constructor|prototype|arguments|caller|name|bind|call|apply|toString|length)$/
          )
        ) { return }
        Reflect.set(
          target,
          prop,
          Reflect.getOwnPropertyDescriptor(source, prop)
        )
      })
  }

  /*  copy all properties of all mixins into aggregation class  */
  mixins.forEach(mixin => {
    copyProps(aggregate.prototype, mixin.prototype)
    copyProps(aggregate, mixin)
  })

  return aggregate
}

Finally, I feel that Reflect is a bit more interesting, nothing more. o((^▽^))o