• Class Declaration & Expression
• Constructor
• Inheritance: extends, super
• Static Methods & Properties
• Class Fields (ES6+ experimental feature)
• get set

OOP Concepts

• Class: A blueprint for creating objects.
• Inheritance: Allows a class to extend another class, inheriting its properties and methods.
• Polymorphism: Different classes can implement the same method in different ways.
• Encapsulation: Bundling data (properties) and behavior (methods) within one unit (class).

class Animal {
  constructor(name) {
    this.name = name;
  }

  speak() {
    console.log(`${this.name} makes a noise.`);
  }
}

class Dog extends Animal {
  speak() {
    console.log(`${this.name} barks.`);
  }
}

const animal = new Animal("Generic Animal");
animal.speak(); // "Generic Animal makes a noise."

const dog = new Dog("Buddy");
dog.speak(); // "Buddy barks."

Singleton Pattern

class.instance

• Ensures that only one instance of a class can exist.

class Singleton {
  constructor() {
    if (Singleton.instance) {
      return Singleton.instance; 
    }
    this.value = 42; 
    Singleton.instance = this;
  }
}

const s1 = new Singleton();
const s2 = new Singleton();

console.log(s1 === s2); // true (both references point to the same instance)

Factory Pattern

• Creates objects without exposing the instantiation logic directly.

class Car {
  constructor() {
    this.type = 'Car';
  }
}

class Truck {
  constructor() {
    this.type = 'Truck';
  }
}

function vehicleFactory(vehicleType) {
  if (vehicleType === 'car') {
    return new Car();
  } else if (vehicleType === 'truck') {
    return new Truck();
  }
  return null;
}

const vehicle1 = vehicleFactory('car');
console.log(vehicle1.type); // "Car"

const vehicle2 = vehicleFactory('truck');
console.log(vehicle2.type); // "Truck"

Observer Pattern