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Interceptors & Middleware 🔧

Note: Interceptors and middleware support is planned for future releases. This article provides a basic workaround until official support is added.

Interceptors allow you to add cross-cutting concerns to your dependency injection system. They let you transform and enhance your services as they're being resolved - perfect for when you need to add some middleware magic to your DI setup.

Basic Workaround​

Until official interceptor support is added, you can achieve similar functionality using factory functions:

// Simple logging wrapper
function withLogging<T>(token: TokenType<T>, factory: () => T): T {
  console.log(`Creating ${token.toString()}`);
  const instance = factory();
  console.log(`Created ${token.toString()}`);
  return instance;
}

// Usage
container.set(USER_SERVICE, {
  useFactory: () => withLogging(USER_SERVICE, () => new UserService()),
});

Advanced Workarounds​

Caching Pattern​

const cache = new Map<string, any>();

function withCaching<T>(token: TokenType<T>, factory: () => T): T {
  const key = token.toString();

  if (cache.has(key)) {
    return cache.get(key);
  }

  const instance = factory();
  cache.set(key, instance);
  return instance;
}

// Usage
container.set(DATABASE, {
  useFactory: () => withCaching(DATABASE, () => new ExpensiveDatabase()),
});

Validation Pattern​

function withValidation<T>(token: TokenType<T>, factory: () => T): T {
  const instance = factory();

  if (!instance) {
    throw new Error(`Service ${token.toString()} resolved to null/undefined`);
  }

  return instance;
}

// Usage
container.set(USER_SERVICE, {
  useFactory: () => withValidation(USER_SERVICE, () => new UserService()),
});

Roadmap​

Official interceptor and middleware support is planned to include:

  • Decorator-based interceptors
  • Middleware chains
  • Performance monitoring
  • Error handling

See the Roadmap for more details on upcoming features.

Next Steps​

These workarounds will keep you productive until the full interceptor system arrives! 🔧✨