Classes in TypeScript provide a way to create reusable, object-oriented code. They bring the structure of traditional object-oriented programming (OOP) to JavaScript with features like inheritance, encapsulation, and abstraction.

Defining a Class

Here’s a basic example:

typescript
const person = new Person("Alice", 30);person.greet(); // "Hello, my name is Alice and I am 30 years old."

Key Features of TypeScript Classes

1. Class Properties

• Properties can be explicitly defined with types.
• Default values can be assigned.

typescript
class Product {  name: string = "Default Product";  price: number = 0;}

2. Constructor

• A special method used to initialize object properties.

typescript
class Car {  make: string;  model: string;  constructor(make: string, model: string) {    class Animal {  public species: string;  private weight: number;  constructor(species: string, weight: number) {    console.log(tiger.getWeight()); // 200

4. Readonly Properties

Properties that can only be set during initialization.

typescript
class Book {  readonly title: string;  constructor(title: string) {    class MathUtils {  static PI: number = 3.14;  static calculateCircumference(radius: number): number {    return 2 * MathUtils.PI * radius;  }}console.log(MathUtils.calculateCircumference(5)); // 31.4

Inheritance

Classes can inherit from other classes using the extends keyword.

typescript
class Employee {  name: string;  constructor(name: string) {    abstract class Shape {  abstract getArea(): number;  describe(): void {    console.log("This is a shape.");  }}class Circle extends Shape {  radius: number;  constructor(radius: number) {    interface Flyable {  fly(): void;}class Bird implements Flyable {  fly(): void {    console.log("The bird is flying.");  }}

Class Example: Real-World Use Case

A Simple Banking System:

typescript
class BankAccount {  private balance: number;  constructor(private accountHolder: string, initialBalance: number) {    class Point {  constructor(public x: number, public y: number) {}}class User {  constructor(public name: string, public age?: number) {}}const user = new User("Alice");console.log(user.age); // undefined

typescript
class Dictionary {  [key: string]: string;}const dict = new Dictionary();dict["hello"] = "world";