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Modules and Facades

Modules let you split your codebase into separate domains. Small applications can use the default Vla.Action, Vla.Service, Vla.Repo and Vla.Resource classes. As your application grows, you can create separate modules with Vla.createModule().

Creating Modules

Section titled “Creating Modules”
import { Vla } from 'vla'


// Default module for smaller apps
class UserService extends Vla.Service {
  // ...
}


// Create separate modules for larger apps
const Users = Vla.createModule("Users")
const Billing = Vla.createModule("Billing")


class UserService extends Users.Service {
  // ...
}


class BillingService extends Billing.Service {
  // ...
}

Cross-Module Communication with Facades

Section titled “Cross-Module Communication with Facades”

Modules cannot directly inject services or repos from other modules. Instead, use Facades as the public interface:

const Users = Vla.createModule("Users")
const Billing = Vla.createModule("Billing")


// Users module
class UserRepo extends Users.Repo {
  db = this.inject(Database)


  findById = this.memo((id: string) => {
    return this.db.users.find({ id })
  })
}


class UserService extends Users.Service {
  repo = this.inject(UserRepo)


  async hasActiveAccount(userId: string) {
    const user = await this.repo.findById(userId)
    return user.status === 'active'
  }
}


// Public facade for other modules
class UsersFacade extends Users.Facade {
  service = this.inject(UserService)


  async hasActiveAccount(userId: string) {
    return this.service.hasActiveAccount(userId)
  }
}


// Billing module
class SubscriptionService extends Billing.Service {
  // ✅ Can inject facades from other modules
  users = this.inject(UsersFacade)


  // ❌ Cannot inject services/repos from other modules
  // users = this.inject(UserService) // This will fail!


  async createSubscription(userId: string) {
    // Use facade to access Users module
    const hasActiveAccount = await this.users.hasActiveAccount(userId)


    if (!hasActiveAccount) {
      throw new Error('User must have active account')
    }


    // Create subscription...
  }
}

Why Facades?

Section titled “Why Facades?”

Facades create a clear boundary between modules:

  • They define the public API of a module
  • They prevent tight coupling between modules
  • They make it clear which functionality is meant for external use vs. internal use

If you find yourself using facades excessively, it might indicate that your domain boundaries need adjustment.

Learn More

Section titled “Learn More”