// 25: class - extends
// To do: make all tests pass, leave the assert lines unchanged!

describe('classes can inherit from another', () => {

  describe('the default super class is Object', () => {

    it('class A is an instance of Object', () => {
      class A extends Object{};

      assert.equal(new A() instanceof Object, true);
    });
 //changed let to class and added extends Objects with {}
    it('B extends A, B is also instance of Object', () => {
      class A extends Object{}
      class B extends A{}

      assert.equal(new B() instanceof A, true);
      assert.equal(new B() instanceof Object, true);
    });

//added "extends Object {}" to class A and added "extends A {}" to class B.
// because A belongs to Objects, B belongs to A => B belongs/instance to Object

    it('class can extend `null`, not an instance of Object', () => {
      class NullClass extends null{}

      let nullInstance = new NullClass();
      assert.equal(nullInstance instanceof Object, false);
    });
//changed 'object' to 'null' on line 26 becuase it is not an instance of Object
  });

  describe('instance of', () => {
    it('when B inherits from A, `new B()` is also an instance of A', () => {
      class A{};
      class B extends A {}

      assert.equal(new B() instanceof A, true);
    });
//changed let to class and added {} because let is a variable (like var) and class defined a blueprint
    it('extend over multiple levels', () => {
      class A {}
      class B extends A {} //added this line to define B belongs to A so C can belongs to B => C belongs to A
      class C extends B {}

      let instance = new C();
// changed 'let instance = C;' by adding 'new' word in front of C with ()
//"new C ()" or "new B ()" defines a real product of the class, while class is just a blueprint (like a construction plan)
      assert.equal(instance instanceof A, true);
    });
  });
});