Extends.js

class Parent {
  x = 1;

  show() {
    alert(this.x);
  }
}

class Child extends Parent {
  x = 2;
}

new Child().show(); // shows 2

MyClass.js

class MyClass {
    x = 1;
    show() {
        alert(this.x);
    }
}

MyClass2.js

class MyClass {
    constructor() {
        super();
        this.x = 1;
    }
    
    show() {
        alert(this.x);
    }
}

refactor.js

class Parent {
  y = 1;
  z = 2;

  get x() { 
    return this.y + this.z; 
  };

  show() {
    alert(this.x);
  }
}

class Child extends Parent {
  x = 2;
}

new Parent().show(); // shows 3 as expected
new Child().show(); // shows 3, but 2 is expected