Dependency Injection

DomusJS is built around explicit dependency injection (DI) using tsyringe, a lightweight, TypeScript-friendly inversion of control (IoC) container.

This approach ensures:

✅ Clear separation of concerns.
✅ Easy testing (you can swap dependencies for mocks).
✅ Extensibility (replace or extend services without rewriting internals).

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What is Dependency Injection?

Dependency injection is a design pattern where:

• Objects do not create their own dependencies.
• Instead, dependencies are provided (injected) by an external container.

This makes your system:

• More modular.
• More testable.
• Less coupled.

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How DomusJS Uses tsyringe

DomusJS configures its services, buses, handlers, and modules through the tsyringe container.

Example:

import { container } from 'tsyringe';
import { InMemoryCommandBus } from '@domusjs/infrastructure';

container.register('CommandBus', {
  useClass: InMemoryCommandBus,
});

When you later resolve:

const commandBus = container.resolve('CommandBus');

You get the same registered instance, fully type-safe.

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Why Not Use Global Singletons?

Using DI allows:

• Isolated instances (if needed).
• Flexible testing setups.
• Cleaner architecture (no hidden globals or magic singletons).

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Registering Dependencies per Context

Each bounded context (like auth, videos, etc.) is responsible for registering its own services in the container.

Example:

container.register<AuthService>('AuthService', {
  useClass: JWTAuthService,
});

This keeps context boundaries clear and avoids leaking dependencies.

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Benefits in DomusJS

• All core modules (auth, jobs, observability, etc.) are injectable.
• Handlers (commands, queries, events) can receive injected services.
• You can replace internal implementations (e.g., swap PinoLogger for your custom logger).

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Learn More

• tsyringe official docs
• How DomusJS Registers Dependencies
• Best Practices for DI in DomusJS