Classes

What is a class?

A class is a blueprint for creating objects that share the same properties and methods.
Under the hood, JavaScript classes are syntactic sugar over the prototype-based inheritance system.

➡ They make code more readable and familiar to object-oriented programmers.

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Declaring a class

A class can contain:

• a constructor → a special function executed when creating the object,
• methods → functions defined within the class.

class Person {
  constructor(name, age) {
    this.name = name;
    this.age = age;
  }

  introduce() {
    console.log(`My name is ${this.name} and I am ${this.age} years old.`);
  }
}

let alice = new Person("Alice", 25);
alice.introduce(); // My name is Alice and I am 25 years old.

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Inheritance

Using extends, a class can inherit from another.
Use super() to call the parent class’s constructor.

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

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

class Dog extends Animal {
  constructor(name, breed) {
    super(name); // calls Animal constructor
    this.breed = breed;
  }

  speak() {
    console.log(`${this.name} barks.`);
  }
}

let rex = new Dog("Rex", "German Shepherd");
rex.speak(); // Rex barks.

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Static methods

A method can be declared static → it is called directly on the class, not on an instance.

class Maths {
  static add(a, b) {
    return a + b;
  }
}

console.log(Maths.add(2, 3)); // 5

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Best practices

• Use classes to model entities (e.g., User, Product).
• Employ extends + super to reuse code and facilitate inheritance.
• Prefer static methods when the action does not depend on a specific instance.
• Keep in mind that classes are syntactic sugar → JavaScript still uses the prototype mechanism under the hood.