Promise.all(
        ['ParentClass.js', 'MemberClass.js'].map(x => System.import(x)))
    .then(([ParentClass, MemberClass]) => {

  function ChildClass() {}

  ChildClass.prototype = new ParentClass();

  ChildClass.prototype.init = function() {

    ParentClass.prototype.init.call(this);

    console.log('child init');
    this.member = new MemberClass().init();

    return this;
  };

  ChildClass.prototype.say = function(something) {
    console.log('ChildClass say: ' + something);
    this.member.say(' also ' + something);
  }

  exports = ChildClass;

});