Maîtriser les types utilitaires TypeScript : un guide pratique pour les développeurs mondiaux

            
interface Customer {
  id: string;
  firstName: string;
  lastName: string;
  email: string;
  phoneNumber: string;
  address: {
    street: string;
    city: string;
    country: string;
    postalCode: string;
  };
  preferences?: {
    language: string;
    currency: string;
  }
}

            

              
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type PartialCustomer = Partial<Customer>;

function updateCustomer(id: string, updates: PartialCustomer): void {
  // ... implémentation pour mettre à jour le client avec l'ID donné
}

updateCustomer("123", { firstName: "John", lastName: "Doe" }); // Valide
updateCustomer("456", { address: { city: "London" } }); // Valide

            

              
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interface AppConfig {
  apiUrl: string;
  theme: string;
  supportedLanguages: string[];
  version: string; // version ajoutée
}

const config: AppConfig = {
  apiUrl: "https://api.example.com",
  theme: "dark",
  supportedLanguages: ["en", "fr", "de", "es", "zh"],
  version: "1.0.0"
};

            

              
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type ReadonlyAppConfig = Readonly<AppConfig>;

const readonlyConfig: ReadonlyAppConfig = {
  apiUrl: "https://api.example.com",
  theme: "dark",
  supportedLanguages: ["en", "fr", "de", "es", "zh"],
  version: "1.0.0"
};

// readonlyConfig.apiUrl = "https://newapi.example.com"; // Erreur : Impossible d'assigner à 'apiUrl' car c'est une propriété en lecture seule.

            

              
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interface Event {
  id: string;
  title: string;
  description: string;
  location: string;
  startTime: Date;
  endTime: Date;
  organizer: string;
  attendees: string[];
}

            

              
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type EventSummary = Pick<Event, "title" | "location" | "startTime">;

function displayEventSummary(event: EventSummary): void {
  console.log(`Événement : ${event.title} à ${event.location} le ${event.startTime}`);
}

            

              
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type NewEvent = Omit<Event, "id">;

function createEvent(event: NewEvent): void {
  // ... implémentation pour créer un nouvel événement
}

            

              
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type Translations = Record<string, string>;

const enTranslations: Translations = {
  "hello": "Hello",
  "goodbye": "Goodbye",
  "welcome": "Welcome to our platform!"
};

const frTranslations: Translations = {
  "hello": "Bonjour",
  "goodbye": "Au revoir",
  "welcome": "Bienvenue sur notre plateforme !"
};

function translate(key: string, language: string): string {
  const translations = language === "en" ? enTranslations : frTranslations; // Simplifié
  return translations[key] || key; // Retour à la clé si aucune traduction n'est trouvée
}

console.log(translate("hello", "en")); // Sortie : Hello
console.log(translate("hello", "fr")); // Sortie : Bonjour
console.log(translate("nonexistent", "en")); // Sortie : nonexistent

            

              
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type EventType = "concert" | "conference" | "workshop" | "webinar";

            

              
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type PhysicalEvent = Exclude<EventType, "webinar">;

// PhysicalEvent est maintenant "concert" | "conference" | "workshop"

function attendPhysicalEvent(event: PhysicalEvent): void {
  console.log(`Participation à un ${event}`);
}

// attendPhysicalEvent("webinar"); // Erreur : L'argument de type '"webinar"' n'est pas assignable au paramètre de type '"concert" | "conference" | "workshop"'.

attendPhysicalEvent("concert"); // Valide

            

              
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type OnlineEvent = Extract<EventType, "webinar">;

// OnlineEvent est maintenant "webinar"

function attendOnlineEvent(event: OnlineEvent): void {
  console.log(`Participation à un ${event} en ligne`);
}

attendOnlineEvent("webinar"); // Valide
// attendOnlineEvent("concert"); // Erreur : L'argument de type '"concert"' n'est pas assignable au paramètre de type '"webinar"'.

            

              
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type MaybeString = string | null | undefined;

type DefinitelyString = NonNullable<MaybeString>;

// DefinitelyString est maintenant string

function processString(str: DefinitelyString): void {
  console.log(str.toUpperCase());
}

// processString(null); // Erreur : L'argument de type 'null' n'est pas assignable au paramètre de type 'string'.
// processString(undefined); // Erreur : L'argument de type 'undefined' n'est pas assignable au paramètre de type 'string'.
processString("hello"); // Valide

            

              
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function greet(name: string): string {
  return `Hello, ${name}!`;
}

type Greeting = ReturnType<typeof greet>;

// Greeting est maintenant string

const message: Greeting = greet("World");

console.log(message);

            

              
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function logEvent(eventName: string, eventData: object): void {
  console.log(`Événement : ${eventName}`, eventData);
}

type LogEventParams = Parameters<typeof logEvent>;

// LogEventParams est maintenant [eventName: string, eventData: object]

const params: LogEventParams = ["user_login", { userId: "123", timestamp: Date.now() }];

logEvent(...params);

            

              
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class Greeter {
  greeting: string;

  constructor(message: string) {
    this.greeting = message;
  }

  greet() {
    return "Hello, " + this.greeting;
  }
}


type GreeterParams = ConstructorParameters<typeof Greeter>;

// GreeterParams est maintenant [message: string]

const paramsGreeter: GreeterParams = ["World"];
const greeterInstance = new Greeter(...paramsGreeter);

console.log(greeterInstance.greet()); // Affiche : Hello, World

            

              
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interface UserProfile {
  name: string;
  age?: number;
  email?: string;
}

type RequiredUserProfile = Required<UserProfile>;

// RequiredUserProfile est maintenant { name: string; age: number; email: string; }

const completeProfile: RequiredUserProfile = {
  name: "Alice",
  age: 30,
  email: "alice@example.com"
};

// const incompleteProfile: RequiredUserProfile = { name: "Bob" }; // Erreur : La propriété 'age' est manquante dans le type '{ name: string; }' mais est requise dans le type 'Required'.

            

              
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type HTTPMethod = "GET" | "POST" | "PUT" | "DELETE";
type APIEndpoint = `/api/users` | `/api/products`;

type RequestURL = `${HTTPMethod} ${APIEndpoint}`;

// RequestURL est maintenant "GET /api/users" | "POST /api/users" | "PUT /api/users" | "DELETE /api/users" | "GET /api/products" | "POST /api/products" | "PUT /api/products" | "DELETE /api/products"

function makeRequest(url: RequestURL): void {
  console.log(`Faire une requête vers ${url}`);
}

makeRequest("GET /api/users"); // Valide
// makeRequest("INVALID /api/users"); // Erreur

            

              
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type UnwrapPromise<T> = T extends Promise<infer U> ? U : T;

// Si T est une Promise<U>, alors le type est U ; sinon, le type est T.

async function fetchData(): Promise<number> {
  return 42;
}


type Data = UnwrapPromise<ReturnType<typeof fetchData>>;

// Data est maintenant number

function processData(data: Data): void {
  console.log(data * 2);
}

processData(await fetchData());

            

              
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interface FormData {
  firstName: string;
  lastName: string;
  email: string;
  country: string; // Requis
  city?: string; // Optionnel
  postalCode?: string;
  newsletterSubscription?: boolean;
}

// Valeurs initiales du formulaire (champs optionnels)
type InitialFormValues = Partial<FormData>;

// Valeurs du formulaire mises à jour (certains champs peuvent être manquants)
type UpdatedFormValues = Partial<FormData>;

// Champs requis pour la soumission
type RequiredForSubmission = Required<Pick<FormData, 'firstName' | 'lastName' | 'email' | 'country'>>;

// Utilisez ces types dans vos composants de formulaire
function initializeForm(initialValues: InitialFormValues): void { }
function updateForm(updates: UpdatedFormValues): void {}
function submitForm(data: RequiredForSubmission): void {}


const initialForm: InitialFormValues = { newsletterSubscription: true };

const updateFormValues: UpdatedFormValues = {
    firstName: "John",
    lastName: "Doe"
};

// const submissionData: RequiredForSubmission = { firstName: "test", lastName: "test", email: "test" }; // ERREUR : 'country' manquant 
const submissionData: RequiredForSubmission = { firstName: "test", lastName: "test", email: "test", country: "USA" }; // OK



            

              
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interface APIResponse {
  user_id: string;
  first_name: string;
  last_name: string;
  email_address: string;
  profile_picture_url: string;
  is_active: boolean;
}

// Transformer la réponse de l'API dans un format plus lisible
type UserData = {
  id: string;
  fullName: string;
  email: string;
  avatar: string;
  active: boolean;
};

function transformApiResponse(response: APIResponse): UserData {
  return {
    id: response.user_id,
    fullName: `${response.first_name} ${response.last_name}`,
    email: response.email_address,
    avatar: response.profile_picture_url,
    active: response.is_active
  };
}

function fetchAndTransformData(url: string): Promise<UserData> {
    return fetch(url)
        .then(response => response.json())
        .then(data => transformApiResponse(data));
}


// Vous pouvez même imposer le type en :

function saferTransformApiResponse(response: APIResponse): UserData {
    const {user_id, first_name, last_name, email_address, profile_picture_url, is_active} = response;
    const transformed: UserData = {
        id: user_id,
        fullName: `${first_name} ${last_name}`,
        email: email_address,
        avatar: profile_picture_url,
        active: is_active
    };

    return transformed;
}


            

              
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interface AppSettings {
  theme: "light" | "dark";
  language: string;
  notificationsEnabled: boolean;
  apiUrl?: string; // URL d'API optionnelle pour différents environnements
  timeout?: number;  //Optionnel
}

// Paramètres par défaut
const defaultSettings: AppSettings = {
  theme: "light",
  language: "en",
  notificationsEnabled: true
};

// Fonction pour fusionner les paramètres utilisateur avec les paramètres par défaut
function mergeSettings(userSettings: Partial<AppSettings>): AppSettings {
  return { ...defaultSettings, ...userSettings };
}

// Utiliser les paramètres fusionnés dans votre application
const mergedSettings = mergeSettings({ theme: "dark", apiUrl: "https://customapi.example.com" });
console.log(mergedSettings);

            

              
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