Inheritance Principle

Inheritance is a way of extending class. The new class (child class) builds logic on the top of the parent class (super class).

Here's an example:

class Vehicle
{
    representation()
    {
        console.log(this.make + " " + this.model);
    }

getInsuranceCost(months)
    {
        return 0;
    }

get make()
    {
        return this._make;
    }

set make(value)
    {
        this._make = value;
    }

get model()
    {
        return this._model;
    }

set model(value)
    {
        this._model = value;
    }
}

// Car inherits Vehicle:
class Car extends Vehicle
{
    // Overwriting method:
    getInsuranceCost(months)
    {
        return months * 25;
    }

// Adding constructor:
    constructor(makeValue, modelValue, doorsCountValue)
    {
        super();

this.make = makeValue;
        this.model = modelValue;
        this.doorsCount = doorsCountValue;
    }

// Method extension:
    representation()
    {
        super.representation();
        console.log( "Doors count: " + this.doorsCount);
    }

// Adding new methods:
    get doorsCount()
    {
        return this._doorsCount;
    }

set doorsCount(value)
    {
        this._doorsCount = value;
    }
}

let car = new Car("Toyota", "Corolla", 4);

// Method that was extended:
car.representation();

console.log("------");
// getter that was added:
console.log(car.doorsCount);
console.log("------");

// Methods that weren't changed:
console.log("Make: " + car.make);
console.log("Model: " + car.model);
console.log("------");

// Method that was overwritten:
console.log("Insurance cost: " +
car.getInsuranceCost(12) + " $");

Output:

Basically the child class can add, extend, rewrite or use the inherited logic from the parent.

For this example:

Added logic:
- parametrized constructor (line 44)
- getter for doorsCount (line 61)
Extended logic:
- representation method (line 54)
Entirely rewritten logic:
- getInsuranceCost (line 38)
Not modified logic:
- getter for make (line 13)
- getter for model (line 23)
- The setters for make and model.