Access Modifiers

JavaScript (ES2022+) supports private fields using # syntax. TypeScript provides private, protected, and public modifiers.

Public (Default)

• Accessible from anywhere.

class User {
  public username: string;
  constructor(username: string) {
    this.username = username;
  }
}

const user = new User("Alice");
console.log(user.username); // Alice

Private (private in TypeScript, # in JavaScript)

• Accessible only within the class.

class Employee {
  #salary: number;
  private tsPrivate = "TS private"; // TypeScript only

  constructor(salary: number) {
    this.#salary = salary;
  }

  getSalary() {
    return this.#salary;
  }
}

const emp = new Employee(5000);
console.log(emp.getSalary()); // ✅ 5000
// console.log(emp.#salary); // JS error: Cannot access private field
// console.log(emp.tsPrivate); // TS error, but still accessible in JS

Protected (protected in TypeScript)

• Accessible in class and subclasses.

class Vehicle {
  protected speed: number;
  constructor(speed: number) {
    this.speed = speed;
  }
}

class Car extends Vehicle {
  accelerate() {
    this.speed += 10;
    console.log(`Accelerated to ${this.speed} km/h`);
  }
}

const car = new Car(50);
car.accelerate(); // Accelerated to 60 km/h
// console.log(car.speed); // Error: 'speed' is protected

Getters & Setters

Getters (get) and setters (set) allow controlled access to class properties.

class Person {
  private _age: number;
  constructor(age: number) {
    this._age = age;
  }

  get age() {
    return this._age;
  }

  set age(value: number) {
    if (value < 0) throw new Error("Age must be positive.");
    this._age = value;
  }
}

const person = new Person(25);
console.log(person.age); // 25
person.age = 30;
console.log(person.age); // 30

Computed Property Example

class Rectangle {
  constructor(private width: number, private height: number) {}

  get area() {
    return this.width * this.height;
  }
}

const rect = new Rectangle(10, 5);
console.log(rect.area); // 50