JavaScript Classes

JavaScript classes provide a structured way to define objects using a blueprint. They use the class keyword and support features like constructors, methods, inheritance, and static properties.

Syntax

class ClassName {
   constructor(parameters) {
       // Initialize properties
   }
   methodName() {
       // Define methods
   }
}

Example

//Creating a Simple Class
class Person {
   constructor(name, age) {
       this.name = name; // Property
       this.age = age;   // Property
   }
   introduce() { // Method
       console.log(`Hi, I'm ${this.name} and I'm ${this.age} years old.`);
   }
}

// Creating an instance of the class
const person1 = new Person("Alice", 30);
person1.introduce();  // Output: Hi, I'm Alice and I'm 30 years old.

• constructor(): This is a special method that initializes the properties when an object is created.
• Methods (introduce()): Functions inside a class that define behaviors.

Class Inheritance (Extending a Class)

Inheritance allows a class to inherit properties and methods from another class using extends.

Example

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

    introduce() {
        console.log(`Hi, I'm ${this.name} and I'm ${this.age} years old.`);
    }
}

// Extending Person Class
class Employee extends Person {
    constructor(name, age, jobTitle) {
        super(name, age); // Calls the Person constructor
        this.jobTitle = jobTitle;
    }

    work() {
        console.log(`${this.name} works as a ${this.jobTitle}.`);
    }
}

// Creating an instance of Employee
const emp1 = new Employee("Bob", 25, "Software Engineer");

emp1.introduce();  // Output: Hi, I'm Bob and I'm 25 years old.
emp1.work();       // Output: Bob works as a Software Engineer.

• extends: Allows a class to inherit from another.
• super(): Calls the parent class's constructor.

Static Methods & Properties

Static methods and properties belong to the class itself, not to instances.

Example

// Using Static Methods
class MathUtils {
   static add(a, b) {
       return a + b;
   }
}
// Calling the static method
console.log(MathUtils.add(5, 3)); // Outputs: 8

static: Defines methods or properties that can be accessed without creating an instance.

Getters and Setters

Getters and setters allow controlled access to class properties.

Example

// Using Getters & Setters
class Circle {
   constructor(radius) {
       this._radius = radius;  // Using `_` to indicate private property
   }
   get radius() {
       return this._radius;
   }
   set radius(value) {
       if (value > 0) {
           this._radius = value;
       } else {
           console.log("Radius must be positive.");
       }
   }
}
const c = new Circle(10);
console.log(c.radius); // 10
c.radius = -5; // Error: Radius must be positive.

• get: Retrieves a property.
• set: Allows controlled modification of a property.