Top 10 NestJS Errors and How to Fix Them

Top 10 NestJS Errors and How to Fix Them

NestJS's dependency injection system is powerful but produces confusing errors. Here are the most common ones and their fixes.

1. Nest can't resolve dependencies

Error: Nest can't resolve dependencies of the UserService (?). 
Please make sure that the argument UserRepository is available.

Fix: Import the module that provides UserRepository:

@Module({
  imports: [TypeOrmModule.forFeature([User])],
  providers: [UserService],
})
export class UserModule {}

2. Circular dependency

Error: A circular dependency has been detected.

Fix: Use forwardRef():

@Module({
  imports: [forwardRef(() => OrderModule)],
})
export class UserModule {}

3. Unknown element in module

Error: UserController is not a controller.

Fix: Ensure the class has the @Controller() decorator.

4. Cannot read properties of undefined (guards)

Usually means the guard can't inject a dependency.

Fix: Make the guard @Injectable() and provide its dependencies:

@Injectable()
export class AuthGuard implements CanActivate {
  constructor(private jwtService: JwtService) {}
}

5. Validation pipe not working

Fix: Install and enable globally:

app.useGlobalPipes(new ValidationPipe({
  whitelist: true,
  transform: true,
}));

6. Cannot GET /route

Route not registered. Fix: Check controller prefix, method decorators, and module imports.

7. Entity metadata not found

Fix: Add your entity to TypeOrmModule.forRoot({ entities: [User] }) or use autoLoadEntities: true.

8. Maximum call stack exceeded

Circular serialization in responses. Fix: Use @Exclude() or custom serializers to break cycles.

9. Cannot set headers after sent

Fix: Ensure middleware calls next() only once and async handlers are properly awaited.

10. Injection token not found

Fix: Use @Inject('TOKEN_NAME') matching the token registered in providers:

providers: [{ provide: 'CONFIG', useValue: config }]
constructor(@Inject('CONFIG') private config: AppConfig) {}

For production NestJS applications, Bugsly captures these runtime errors with full dependency injection context, making it much easier to diagnose issues that only surface in production environments.