Bun Server Troubleshooting

Dependency Injection Issues

“Parameter type is undefined” Error

Symptom:

Error: Cannot resolve dependency at index 0 of MyController.
Parameter type is undefined. Use @Inject() decorator to specify the dependency type.

Causes:

1. Missing tsconfig.json configuration
2. Monorepo root missing tsconfig.json
3. Debug plugin not reading tsconfig.json

Solution:

Ensure tsconfig.json includes:

{
  "compilerOptions": {
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true
  }
}

For monorepo projects, add tsconfig.json to root directory.

Workaround: Use explicit @Inject():

constructor(@Inject(UserService) private userService: UserService) {}

“Provider not found for token” Error

Symptom:

Error: Provider not found for token: Symbol(@dangao/bun-server:events:emitter)

Cause: Module requiring forRoot() was not configured.

Solution:

// ❌ Wrong
@Module({
  imports: [EventModule],
})

// ✅ Correct
@Module({
  imports: [EventModule.forRoot({ wildcard: true })],
})

EventModule Issues

@OnEvent Decorator Not Working

Cause: Event listeners not initialized.

Solution: Call initializeListeners after registerModule:

import { Application, EventModule, ModuleRegistry } from "@dangao/bun-server";

const app = new Application({ port: 3100 });
app.registerModule(AppModule);

// Initialize event listeners
const rootModuleRef = ModuleRegistry.getInstance().getModuleRef(AppModule);
if (rootModuleRef?.container) {
  EventModule.initializeListeners(
    rootModuleRef.container,
    [NotificationListener, AuditListener], // All @OnEvent classes
  );
}

app.listen();

Application Startup Issues

Module Configuration Order

Problem: Child modules fail to resolve dependencies.

Solution: Configure forRoot() before module definitions:

// ✅ Configure first
EventModule.forRoot({ wildcard: true });
LoggerModule.forRoot({ level: LogLevel.INFO });

// Then define modules
@Module({
  imports: [EventModule],
  providers: [UserService],
})
class UserModule {}

Circular Dependencies

Symptom: Stack overflow or undefined services.

Solution: Use forwardRef:

@Injectable()
class ServiceA {
  constructor(
    @Inject(forwardRef(() => ServiceB)) private b: ServiceB
  ) {}
}

Debug Techniques

Verify Decorator Metadata

import "reflect-metadata";

// Check if paramtypes are generated
console.log(
  "paramTypes:",
  Reflect.getMetadata("design:paramtypes", YourController)
);
// Expected: [class ServiceA, class ServiceB, ...]
// Problem: undefined or []

Debug Container Resolution

const container = app.getContainer();

// List all registered providers
console.log("Providers:", container.getProviders());

// Try manual resolution
try {
  const service = container.resolve(UserService);
  console.log("Resolved:", service);
} catch (error) {
  console.error("Resolution failed:", error);
}

Debug Module References

import { ModuleRegistry } from "@dangao/bun-server";

const moduleRef = ModuleRegistry.getInstance().getModuleRef(AppModule);
console.log("Module container:", moduleRef?.container);
console.log("Module metadata:", moduleRef?.metadata);

Common Mistakes

Forgetting @Injectable

// ❌ Missing decorator
class UserService {
  getUser() { return {}; }
}

// ✅ Correct
@Injectable()
class UserService {
  getUser() { return {}; }
}

Using import type with Symbol+Interface Pattern

// ❌ Wrong - type-only import removes Symbol at runtime
import type { UserService } from "./user.service";

// ✅ Correct - keeps both interface and Symbol
import { UserService } from "./user.service";

Not Exporting from Module

// ❌ Service not accessible to other modules
@Module({
  providers: [SharedService],
})
class SharedModule {}

// ✅ Export to make available
@Module({
  providers: [SharedService],
  exports: [SharedService],
})
class SharedModule {}

Debugging Checklist

1. tsconfig.json has experimentalDecorators: true
2. tsconfig.json has emitDecoratorMetadata: true
3. Services have @Injectable() decorator
4. Modules using forRoot() are configured before definitions
5. Services are registered in module providers
6. Required services are in module exports
7. Event listeners call EventModule.initializeListeners()

Related Resources

• DI Injection Not Working
• EventModule Setup
• Troubleshooting Docs