Careeroza

Classes and Objects

Declaring a Class

A class is a blueprint for objects. In TypeScript you declare each property with its type. With strict mode every property must be initialised (in the declaration or in the constructor).

Example

class Product {
  name: string;
  price: number;
  stock = 0; // type inferred as number

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

const p1 = new Product("Desk Lamp", 899);
p1.stock = 25;
const p2 = new Product("Notebook", 60);

console.log(p1);
console.log(p2.name, p2.stock);

Output

Product { name: 'Desk Lamp', price: 899, stock: 25 }
Notebook 0

Uninitialised Property

Example

With strictPropertyInitialization (part of strict) a property that is never set is error TS2564.

class Product {
  name: string;
  price: number;

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

Compiler output (tsc)

Line 3: error TS2564: Property 'price' has no initializer and is not definitely assigned in the constructor.