Typed Classes

Syntax

class Name {
  property: type;
  constructor(param: type) { }
}

Examples

class User {
  id: number;
  name: string;
  email: string;

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

  describe(): string {
    return `${this.name} (${this.email})`;
  }
}

const user = new User(1, "Alice", "alice@example.com");
console.log(user.describe());

class Product {
  constructor(
    public id: number,
    public name: string,
    private price: number
  ) {
    // TypeScript automatically creates and assigns these three properties -
    // no need to repeat "this.id = id" etc manually
  }

  getPrice(): number {
    return this.price;
  }
}

const product = new Product(1, "Laptop", 999);
console.log(product.name);      // accessible - public
// console.log(product.price);   // Error - private

Best practices

• Use parameter properties (public/private directly in the constructor signature) to reduce repetitive boilerplate for simple classes
• Type every class property explicitly, or initialize it with a value TypeScript can infer from - uninitialized untyped properties default to any implicitly, weakening safety
• Keep constructors focused on initialization - complex setup logic is often clearer in a separate method or factory function
• Use readonly on properties that should be set once in the constructor and never modified afterward

At a glance

Purpose

Static types for JavaScript

File extension

.ts · .tsx

Runs in

Compiled to JavaScript

Usually used with

JavaScript and its ecosystem

Specifications & further reading

• TypeScript Handbook

Related TypeScript documentation