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TypeScript class - GeeksforGeeks

Last Updated : 23 Jan, 2025

A TypeScript class is a blueprint for creating objects, encapsulating properties (data) and methods (behavior) to promote organization, reusability, and readability.

• Supports inheritance, allowing one class to extend another and reuse functionality.
• Provides access modifiers (public, private, protected) to control member accessibility and enforce encapsulation.

class Person {
  name: string;
  age: number;

  constructor(name: string, age: number) {
    this.name = name;
    this.age = age;
  }

  introduce(): string {
    return `Hi, my name is ${this.name} and I am ${this.age} years old.`;
  }
}

const person1 = new Person("Alice", 25);
console.log(person1.introduce());

• The Person class defines properties name and age, a constructor for initialization, and a method introduce to return a greeting message.
• An object person1 is created from the class, and the introduce method is called to output a personalized message.

Hi, my name is Alice and I am 25 years old.

In TypeScript, classes are blueprints for creating objects. They encapsulate data (properties) and behavior (methods) into a single unit. By defining classes, you can organize your code, promote reusability, and enhance readability.

• Methods: Functions defined within a class that perform specific actions.
• Constructors: Special methods called when an object is created from a class. Constructors initialize class properties.
• Properties: Variables associated with a class instance.
• Inheritance: The ability to create new classes based on existing ones, allowing code reuse and specialization.

• public: Properties and methods are accessible from outside the class.
• private: Restricts access to within the class itself.
• protected: Allows access within the class and its subclasses.

A constructor is a special method within a class that is automatically invoked when we create an instance of that class. Its primary purpose is to initialize the properties of the current instance. In TypeScript, constructors allow us to set up the initial state of an object.

class Person {
    constructor(public name: string, public age: number) {
        // Initialize properties
    }
}

const john = new Person('Uday', 20);
console.log(`Name: ${john.name}, Age: ${john.age}`);

Output:

[LOG]: "Name: Uday, Age: 20" 

Objects An object is an instance of class which contains set of key value pairs. It's value may be scalar values or functions or even array of other objects. 

Syntax

 let obj = {
    key1: value1,
    key2: value2,
    // ...
};

A class’s attributes and functions can be accessed by the object. With the help of ‘ . ’ dot notation or bracket notation(['']) we access the data members of a class.

//accessing an attribute 
obj.field_name or obj['field_name']
//accessing a function 
obj.function_name()

The Person class has name and age properties set through its constructor. It includes a greet method to log a greeting with these details. Instances like person can access attributes and methods defined within the class.

class Person {
    name: string;
    age: number;

    constructor(name: string, age: number) {
        this.name = name;
        this.age = age;
    }

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

const person = new Person('Rahul', 22);
console.log(person.name); // Accessing attribute
person.greet();           // Accessing function

Output:

Rahul
Hello, I'm Rahul and I'm 22 years old.

More Example of TypeScript Classes

class BankAccount {
  accountHolder: string;
  balance: number;

  constructor(accountHolder: string, initialBalance: number) {
    this.accountHolder = accountHolder;
    this.balance = initialBalance;
  }

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

  getBalance(): string {
    return `The balance for ${this.accountHolder} is $${this.balance}`;
  }
}

const account = new BankAccount("John Doe", 500);
account.deposit(200);
console.log(account.getBalance());

• The BankAccount class allows for creating an account, adding deposits, and checking the balance.
• account.deposit(200) adds $200 to the initial balance of $500, and getBalance displays the updated balance.

Output:

The balance for John Doe is $700

class Rectangle {
  width: number;
  height: number;

  constructor(width: number, height: number) {
    this.width = width;
    this.height = height;
  }

  calculateArea(): number {
    return this.width * this.height;
  }
}

const rect = new Rectangle(10, 5);
console.log(`Area of the rectangle: ${rect.calculateArea()}`);

• The Rectangle class calculates the area of a rectangle using its width and height.
• calculateArea() is invoked on the rectangle object to compute the area.

Ouptut:

Area of the rectangle: 50

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