Interfaces and Advanced Types

Interfaces and custom types are at the heart of TypeScript. They let you define the shape of your data and create clear contracts in your code.

Basic Interfaces

Defining an Interface

interface Utilisateur {
  id: number;
  nom: string;
  email: string;
  age: number;
}

// Usage
let utilisateur: Utilisateur = {
  id: 1,
  nom: "Alice",
  email: "alice@example.com",
  age: 30
};

Optional Properties

interface Produit {
  id: number;
  nom: string;
  prix: number;
  description?: string; // Optional property
  enStock?: boolean;
}

let produit1: Produit = {
  id: 1,
  nom: "Ordinateur",
  prix: 999
  // description and enStock are optional
};

let produit2: Produit = {
  id: 2,
  nom: "Souris",
  prix: 25,
  description: "Souris ergonomique",
  enStock: true
};

Read-Only Properties

interface Configuration {
  readonly apiUrl: string;
  readonly version: string;
  timeout: number;
}

let config: Configuration = {
  apiUrl: "https://api.example.com",
  version: "1.0.0",
  timeout: 5000
};

// config.apiUrl = "nouvelle-url"; // ❌ Error: read-only property
config.timeout = 10000; // ✅ OK