text: class Base {
    constructor() {
      this.base = ()=>'base'
    }
  }
  class Demo1 extends Base  {
    foo () {
      return [this.base(), "foo"];
    }
  }
  class Demo2 extends Base  {
    constructor() {
      super();
      this.bar = ()=>'bar';
    }
    foo () {
      return [this.base(), this.bar()];
    }
  }
  export default function demo() {
    return [new Demo1().foo(), new Demo2().foo()];
  }