class Test {
  setPoints() {
    this.x = 20;
    this.y = 40;
  }
  getPoints() {
    const { x, y } = this;
    return { x, y };
  }
}

class SubTest extends Test {
  // Override class method, call base class method using super
  // setPoints() {
  //   super.setPoints();
  //   this.x = 10;
  // }
}

SubTest.prototype.originalSetPoints = SubTest.prototype.setPoints;
SubTest.prototype.setPoints = function () {
  this.originalSetPoints();
  this.x = 10;
};

const test = new SubTest();

test.setPoints();
console.log(test.getPoints());