TypeScript Classes

Building blocks for object-oriented programming

🏗️ What are TypeScript Classes?

Classes are blueprints for creating objects with properties and methods. They help organize code by grouping related data and functions together, making your programs more structured and reusable. 


// Simple class example
class Person {
    name: string;
    age: number;
}

const john = new Person();
john.name = "John";
john.age = 25;

Output:

Person { name: "John", age: 25 }

Key Class Concepts

📦

Properties

Variables that belong to a class 

class Car {
    brand: string;
    model: string;
}
⚙️

Methods

Functions that belong to a class 

class Dog {
    bark() {
        return "Woof!";
    }
}
🎯

Objects

Instances created from classes 

const myCar = new Car();
myCar.brand = "Toyota";
🔒

Access Modifiers

Control property visibility 

class User {
    public name: string;
    private password: string;
}

🔹 Creating a Basic Class

Here's how to define and use a simple class: 

class Student {
    name: string;
    grade: number;

    study() {
        return `${this.name} is studying`;
    }
}

// Create an object
const student1 = new Student();
student1.name = "Alice";
student1.grade = 10;

console.log(student1.study());

Output:

Alice is studying

🔹 Class with Properties and Methods

Combine data and behavior in one class: 

class Calculator {
    result: number = 0;

    add(num: number) {
        this.result += num;
        return this;
    }

    subtract(num: number) {
        this.result -= num;
        return this;
    }

    getResult() {
        return this.result;
    }
}

const calc = new Calculator();
calc.add(10).subtract(3);
console.log(calc.getResult());

Output:

7

🔹 Access Modifiers

Control who can access class members: 

class BankAccount {
    public accountHolder: string;
    private balance: number = 0;
    protected accountNumber: string;

    public deposit(amount: number) {
        this.balance += amount;
    }

    public getBalance() {
        return this.balance;
    }
}

const account = new BankAccount();
account.accountHolder = "John Doe";
account.deposit(1000);
console.log(account.getBalance());
// account.balance = 5000; // Error: private property

Output:

1000

  • public: Accessible everywhere (default)
  • private: Only accessible within the class
  • protected: Accessible in class and subclasses

🔹 Readonly Properties

Create properties that cannot be changed after initialization: 

class Book {
    readonly isbn: string;
    title: string;

    constructor(isbn: string, title: string) {
        this.isbn = isbn;
        this.title = title;
    }
}

const book = new Book("978-0-123456-78-9", "TypeScript Guide");
console.log(book.isbn);
// book.isbn = "new-isbn"; // Error: readonly property

Output:

978-0-123456-78-9

🧠 Test Your Knowledge

What keyword is used to create an instance of a class?