Import ed export di soli tipi

Benvenuto

Perché i soli tipi sono importanti

import { User } from './models'; // includes runtime binding
import type { User } from './models'; // compile-time only, erased

Sintassi per import type

import type { ApiResponse } from './api-types';

function handleResponse(res: ApiResponse<User>): void {
  // ApiResponse used as type annotation only
}

Sintassi per export type

// user.types.ts
export type UserId = string;
export type { User, UserRole };

Import di tipo inline

import { type User, createUser } from './user';
// User is type-only, createUser is a runtime value

Risoluzione delle dipendenze circolari

verbatimModuleSyntax

// tsconfig.json
{ "compilerOptions": { "verbatimModuleSyntax": true } }

importsNotUsedAsValues

Vantaggi nei bundler

Riesportazioni di soli tipi

// public-api.ts
export type { User, UserRole } from './internal-user';
export { createUser } from './internal-user'; // runtime

Errore: impossibile usare import type come valore

import type { User } from './user';
// const u = new User(); // Error — User was imported as type-only

Controllo rapido

Riepilogo