Inheritance is another main OOP principle, which means that some classes can adopt properties of other classes, and maybe extend them.

Like, for example, we have class `Rectangle` which represents the rectangle instance. Then, let’s define class `Square`. Square is a Rectangle, too, so we can create this class from the `Rectangle` class. Use keyword `extends`:

class Rectangle {
  height;
  width;
  constructor(height, width) {
    this.height = height;
    this.width = width;
    console.log('Rectangle created');
  }
}

class Square extends Rectangle{
}

Now `Square` has the same attributes and methods as `Rectangle` class.

The `Rectangle` is a base class, and `Square` is a derived class. Or you can say that `Rectangle` is a **parent class** and `Square` is a **daughter class**.

`Square` differs with sides length: height is equal to the width, unlike for `Rectangle`.

Usually, JavaScript classes such as an `array`, `console`, `window`, etc. inherit some base classes, which can inherit other classes. It is very advisable to extend existing classes, not to define similar classes again. 

Every programmer should be familiar with OOP principles. If basic JavaScript syntax doesn't scare you and you want to develop your projects, start learning OOP right now!

Object is the first 'O' in Object-Oriented Programming. Let's create one.

The encapsulation is next OOP principle, that help to control and validate the behavior of the class and objects.

Learn how to detect if the field should be static.

Learn why some classes are parents of other classes.

What is an Inheritance

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