title: Call child method class in parent with parent instance
body: <p>I don't want my parent class to be too long so I separate some methods from it and create child class. </p>
  
  <p>However I don't want to use child class as a instance I want it to be used only by parent class.</p>
  
  <pre><code>class Parent {
    parentMethod() {
      this.foo(); // execute from parent
    }
  }
  
  class Child extends Parent {
    foo() {
      console.log('foo!');
    }
  }
  
  const parent = new Parent();
  parent.parentMethod(); // execute parent method which execute child method
  </code></pre>
  
  <p>this cause:</p>
  
  <blockquote>
    <p>Uncaught TypeError: this.foo is not a function</p>
  </blockquote>