Typescript IoC (Inversion Of Control) container

Advantages

• battle tested :boom:
• written on typescript
• simple and lightweight :heart:
• clean API :green_heart:
• supports tagged scopes
• fully test covered :100:
• can be used with decorators @inject
• can inject properties
• can inject lazy dependencies
• composable and open to extend

Content

• Setup
• Quickstart
• Cheatsheet
• Recipes
• Container
  • Basic usage
  • Scope tags
  • Dynamic Tag Management addTags
  • Instances
  • Dispose
  • Lazy lazy
  • Lazy with registerPipe lazy()
• Injector
  • Metadata @inject
  • Simple
  • Proxy
• Provider provider
  • Singleton singleton
  • Arguments args argsFn
  • Visibility visible
  • Alias asAlias
  • Decorator decorate
• Registration @register
  • Key asKey
  • Scope scope
• Module
• Hook @hook
  • OnConstruct @onConstruct
  • OnDispose @onDispose
  • Inject Property
  • Inject Method
• Mock
• Error

Setup

npm install ts-ioc-container reflect-metadata

yarn add ts-ioc-container reflect-metadata

Just put it in the entrypoint file of your project. It should be the first line of the code.

import 'reflect-metadata';

And tsconfig.json should have next options:

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

Quickstart

import 'reflect-metadata';
import { Container, register, bindTo, singleton } from 'ts-ioc-container';

@register(bindTo('ILogger'), singleton())
class Logger {
  log(message: string) {
    console.log(message);
  }
}

class App {
  constructor(private logger = container.resolve<Logger>('ILogger')) {}
  start() {
    this.logger.log('hello');
  }
}

const container = new Container({ tags: ['application'] }).addRegistration(Logger);
container.resolve(App).start();

Cheatsheet

• Register class with key: @register(bindTo('Key')) class Service {}
• Register value: R.fromValue(config).bindToKey('Config')
• Singleton: @register(singleton())
• Scoped registration: @register(scope((s) => s.hasTag('request')))
• Resolve by alias: container.resolveByAlias('Alias')
• Current scope token: select.scope.current
• Lazy token: select.token('Service').lazy()
• Inject decorator: @inject('Key')
• Property inject: injectProp(target, 'propName', select.token('Key'))

Recipes

Express/Next handler (per-request scope)

const app = new Container({ tags: ['application'] })
  .addRegistration(R.fromClass(Logger).pipe(singleton()));

function handleRequest() {
  const requestScope = app.createScope({ tags: ['request'] });
  const logger = requestScope.resolve<Logger>('Logger');
  logger.log('req started');
}

Background worker (singleton client, transient jobs)

@register(singleton())
class QueueClient {}

class JobHandler {
  constructor(@inject('QueueClient') private queue: QueueClient) {}
}

const worker = new Container({ tags: ['worker'] })
  .addRegistration(R.fromClass(QueueClient))
  .addRegistration(R.fromClass(JobHandler));

Frontend widget/page scope with lazy dependency

@register(bindTo('FeatureFlags'), singleton())
class FeatureFlags {
  load() { /* fetch flags */ }
}

class Widget {
  constructor(@inject(select.token('FeatureFlags').lazy()) private flags: FeatureFlags) {}
}

const page = new Container({ tags: ['page'] })
  .addRegistration(R.fromClass(FeatureFlags))
  .addRegistration(R.fromClass(Widget));

Container

IContainer consists of:

• Provider is dependency factory which creates dependency
• Injector describes how to inject dependencies to constructor
• Registration is provider factory which registers provider in container

Basic usage

import 'reflect-metadata';
import { Container, type IContainer, inject, Registration as R, select } from 'ts-ioc-container';

/**
 * User Management Domain - Basic Dependency Injection
 *
 * This example demonstrates how to wire up a simple authentication service
 * that depends on a user repository. This pattern is common in web applications
 * where services need database access.
 */
describe('Basic usage', function () {
  // Domain types
  interface User {
    id: string;
    email: string;
    passwordHash: string;
  }

  // Repository interface - abstracts database access
  interface IUserRepository {
    findByEmail(email: string): User | undefined;
  }

  // Concrete implementation
  class UserRepository implements IUserRepository {
    private users: User[] = [{ id: '1', email: '[email protected]', passwordHash: 'hashed_password' }];

    findByEmail(email: string): User | undefined {
      return this.users.find((u) => u.email === email);
    }
  }

  it('should inject dependencies', function () {
    // AuthService depends on IUserRepository
    class AuthService {
      constructor(@inject('IUserRepository') private userRepo: IUserRepository) {}

      authenticate(email: string): boolean {
        const user = this.userRepo.findByEmail(email);
        return user !== undefined;
      }
    }

    // Wire up the container
    const container = new Container().addRegistration(R.fromClass(UserRepository).bindTo('IUserRepository'));

    // Resolve AuthService - UserRepository is automatically injected
    const authService = container.resolve(AuthService);

    expect(authService.authenticate('[email protected]')).toBe(true);
    expect(authService.authenticate('[email protected]')).toBe(false);
  });

  it('should inject current scope for request context', function () {
    // In Express.js, each request gets its own scope
    // Services can access the current scope to resolve request-specific dependencies
    const appContainer = new Container({ tags: ['application'] });

    class RequestHandler {
      constructor(@inject(select.scope.current) public requestScope: IContainer) {}

      handleRequest(): string {
        // Access request-scoped dependencies
        return this.requestScope.hasTag('application') ? 'app-scope' : 'request-scope';
      }
    }

    const handler = appContainer.resolve(RequestHandler);

    expect(handler.requestScope).toBe(appContainer);
    expect(handler.handleRequest()).toBe('app-scope');
  });
});

Scope

Sometimes you need to create a scope of container. For example, when you want to create a scope per request in web application. You can assign tags to scope and provider and resolve dependencies only from certain scope.

• NOTICE: remember that when scope doesn't have dependency then it will be resolved from parent container
• NOTICE: when you create a scope of container then all providers are cloned to new scope. For that reason every provider has methods clone and isValid to clone itself and check if it's valid for certain scope accordingly.
• NOTICE: when you create a scope then we clone ONLY tags-matched providers.

import 'reflect-metadata';
import {
  bindTo,
  Container,
  DependencyNotFoundError,
  type IContainer,
  inject,
  register,
  Registration as R,
  scope,
  select,
  singleton,
} from 'ts-ioc-container';

/**
 * User Management Domain - Request Scopes
 *
 * In web applications, each HTTP request typically gets its own scope.
 * This allows request-specific data (current user, request ID, etc.)
 * to be isolated between concurrent requests.
 *
 * Scope hierarchy:
 *   Application (singleton services)
 *     └── Request (per-request services)
 *           └── Transaction (database transaction boundary)
 */

// SessionService is only available in request scope - not at application level
@register(bindTo('ISessionService'), scope((s) => s.hasTag('request')), singleton())
class SessionService {
  private userId: string | null = null;

  setCurrentUser(userId: string) {
    this.userId = userId;
  }

  getCurrentUserId(): string | null {
    return this.userId;
  }
}

describe('Scopes', function () {
  it('should isolate request-scoped services', function () {
    // Application container - lives for entire app lifetime
    const appContainer = new Container({ tags: ['application'] }).addRegistration(R.fromClass(SessionService));

    // Simulate two concurrent HTTP requests
    const request1Scope = appContainer.createScope({ tags: ['request'] });
    const request2Scope = appContainer.createScope({ tags: ['request'] });

    // Each request has its own SessionService instance
    const session1 = request1Scope.resolve<SessionService>('ISessionService');
    const session2 = request2Scope.resolve<SessionService>('ISessionService');

    session1.setCurrentUser('user-1');
    session2.setCurrentUser('user-2');

    // Sessions are isolated - user data doesn't leak between requests
    expect(session1.getCurrentUserId()).toBe('user-1');
    expect(session2.getCurrentUserId()).toBe('user-2');
    expect(session1).not.toBe(session2);

    // SessionService is NOT available at application level (security!)
    expect(() => appContainer.resolve('ISessionService')).toThrow(DependencyNotFoundError);
  });

  it('should create child scopes for transactions', function () {
    const appContainer = new Container({ tags: ['application'] });

    // RequestHandler can create a transaction scope for database operations
    class RequestHandler {
      constructor(@inject(select.scope.create({ tags: ['transaction'] })) public transactionScope: IContainer) {}

      executeInTransaction(): boolean {
        // Transaction scope inherits from request scope
        // Database operations can be rolled back together
        return this.transactionScope.hasTag('transaction');
      }
    }

    const handler = appContainer.resolve(RequestHandler);

    expect(handler.transactionScope).not.toBe(appContainer);
    expect(handler.transactionScope.hasTag('transaction')).toBe(true);
    expect(handler.executeInTransaction()).toBe(true);
  });
});

Dynamic Tag Management

You can dynamically add tags to a container after it's been created using the addTags() method. This is useful for environment-based configuration, feature flags, and progressive container setup.

• Tags can be added one at a time or multiple at once
• Tags must be added before registrations are applied - scope matching happens at registration time
• Useful for conditional configuration based on NODE_ENV or runtime flags
• Container can be configured incrementally as the application initializes

import { bindTo, Container, register, Registration as R, scope } from 'ts-ioc-container';

describe('addTags', () => {
  it('should dynamically add tags to enable environment-based registration', () => {
    @register(bindTo('logger'), scope((s) => s.hasTag('development')))
    class ConsoleLogger {
      log(message: string) {
        console.log(`[DEV] ${message}`);
      }
    }

    @register(bindTo('logger'), scope((s) => s.hasTag('production')))
    class FileLogger {
      log(message: string) {
        console.log(`[PROD] ${message}`);
      }
    }

    // Create container and configure for environment
    const container = new Container();
    const environment = 'development';
    container.addTags(environment); // Add tag dynamically based on environment

    // Register services after tag is set
    container.addRegistration(R.fromClass(ConsoleLogger)).addRegistration(R.fromClass(FileLogger));

    // Resolve logger - gets ConsoleLogger because 'development' tag was added
    const logger = container.resolve<ConsoleLogger>('logger');
    expect(logger).toBeInstanceOf(ConsoleLogger);
  });

  it('should add multiple tags for feature-based configuration', () => {
    @register(bindTo('premiumFeature'), scope((s) => s.hasTag('premium')))
    class PremiumFeature {}

    @register(bindTo('betaFeature'), scope((s) => s.hasTag('beta')))
    class BetaFeature {}

    const container = new Container();

    // Add multiple tags at once
    container.addTags('premium', 'beta', 'experimental');

    // Verify all tags are present
    expect(container.hasTag('premium')).toBe(true);
    expect(container.hasTag('beta')).toBe(true);
    expect(container.hasTag('experimental')).toBe(true);

    // Register features after tags are added
    container.addRegistration(R.fromClass(PremiumFeature)).addRegistration(R.fromClass(BetaFeature));

    // Both features are available because container has both tags
    expect(container.resolve('premiumFeature')).toBeInstanceOf(PremiumFeature);
    expect(container.resolve('betaFeature')).toBeInstanceOf(BetaFeature);
  });

  it('should affect child scope creation', () => {
    @register(bindTo('service'), scope((s) => s.hasTag('api')))
    class ApiService {
      handleRequest() {
        return 'API response';
      }
    }

    const appContainer = new Container();

    // Add tag to parent
    appContainer.addTags('api');
    appContainer.addRegistration(R.fromClass(ApiService));

    // Create child scopes - they inherit parent's registrations
    const requestScope1 = appContainer.createScope({ tags: ['request'] });
    const requestScope2 = appContainer.createScope({ tags: ['request'] });

    // Both scopes can access the ApiService from parent
    expect(requestScope1.resolve<ApiService>('service').handleRequest()).toBe('API response');
    expect(requestScope2.resolve<ApiService>('service').handleRequest()).toBe('API response');
  });

  it('should enable incremental tag addition', () => {
    const container = new Container();

    // Start with basic tags
    container.addTags('application');
    expect(container.hasTag('application')).toBe(true);

    // Add more tags as needed
    container.addTags('monitoring', 'logging');
    expect(container.hasTag('monitoring')).toBe(true);
    expect(container.hasTag('logging')).toBe(true);

    // All tags are retained
    expect(container.hasTag('application')).toBe(true);
  });
});

Instances

Sometimes you want to get all instances from container and its scopes. For example, when you want to dispose all instances of container.

• you can get instances from container and scope which were created by injector

import { bindTo, Container, inject, register, Registration as R, select } from 'ts-ioc-container';

/**
 * User Management Domain - Instance Collection
 *
 * Sometimes you need access to all instances of a certain type:
 * - Collect all active database connections for health checks
 * - Gather all loggers to flush buffers before shutdown
 * - Find all request handlers for metrics collection
 *
 * The `select.instances()` token resolves all created instances,
 * optionally filtered by a predicate function.
 */
describe('Instances', function () {
  @register(bindTo('ILogger'))
  class Logger {}

  it('should collect instances across scope hierarchy', () => {
    // App that needs access to all logger instances (e.g., for flushing)
    class App {
      constructor(@inject(select.instances()) public loggers: Logger[]) {}
    }

    const appContainer = new Container({ tags: ['application'] }).addRegistration(R.fromClass(Logger));
    const requestScope = appContainer.createScope({ tags: ['request'] });

    // Create loggers in different scopes
    appContainer.resolve('ILogger');
    requestScope.resolve('ILogger');

    const appLevel = appContainer.resolve(App);
    const requestLevel = requestScope.resolve(App);

    // Request scope sees only its own instance
    expect(requestLevel.loggers.length).toBe(1);
    // Application scope sees all instances (cascades up from children)
    expect(appLevel.loggers.length).toBe(2);
  });

  it('should return only current scope instances when cascade is disabled', () => {
    // Only get instances from current scope, not parent scopes
    class App {
      constructor(@inject(select.instances().cascade(false)) public loggers: Logger[]) {}
    }

    const appContainer = new Container({ tags: ['application'] }).addRegistration(R.fromClass(Logger));
    const requestScope = appContainer.createScope({ tags: ['request'] });

    appContainer.resolve('ILogger');
    requestScope.resolve('ILogger');

    const appLevel = appContainer.resolve(App);

    // Only application-level instance, not request-level
    expect(appLevel.loggers.length).toBe(1);
  });

  it('should filter instances by predicate', () => {
    const isLogger = (instance: unknown) => instance instanceof Logger;

    class App {
      constructor(@inject(select.instances(isLogger)) public loggers: Logger[]) {}
    }

    const container = new Container({ tags: ['application'] }).addRegistration(R.fromClass(Logger));

    const logger0 = container.resolve('ILogger');
    const logger1 = container.resolve('ILogger');
    const app = container.resolve(App);

    expect(app.loggers).toHaveLength(2);
    expect(app.loggers[0]).toBe(logger0);
    expect(app.loggers[1]).toBe(logger1);
  });
});

Check Registration

Sometimes you want to check if a registration with a specific key exists in the container. This is useful for conditional registration logic, validation, and debugging.

• hasRegistration(key) checks if a registration exists in the current container or parent containers
• Checks both the current container's registrations and parent container registrations
• Works with string keys, symbol keys, and token keys
• Returns false after container disposal

import { Container, Registration as R, bindTo, register, SingleToken } from 'ts-ioc-container';

/**
 * Container Registration Checking - hasRegistration
 *
 * The `hasRegistration` method allows you to check if a registration with a specific key
 * exists in the current container. This is useful for conditional registration logic,
 * validation, and debugging.
 *
 * Key points:
 * - Checks only the current container's registrations (not parent containers)
 * - Works with string keys, symbol keys, and token keys
 * - Returns false after container disposal
 * - Useful for conditional registration patterns
 */
describe('hasRegistration', function () {
  const createAppContainer = () => new Container({ tags: ['application'] });

  it('should return true when registration exists with string key', function () {
    const container = createAppContainer();
    container.addRegistration(R.fromValue('production').bindToKey('Environment'));

    expect(container.hasRegistration('Environment')).toBe(true);
  });

  it('should return false when registration does not exist', function () {
    const container = createAppContainer();

    expect(container.hasRegistration('NonExistentService')).toBe(false);
  });

  it('should work with symbol keys', function () {
    const container = createAppContainer();
    const serviceKey = Symbol('IService');
    container.addRegistration(R.fromValue({ name: 'Service' }).bindToKey(serviceKey));

    expect(container.hasRegistration(serviceKey)).toBe(true);
  });

  it('should work with token keys', function () {
    const container = createAppContainer();
    const loggerToken = new SingleToken<{ log: (msg: string) => void }>('ILogger');
    container.addRegistration(R.fromValue({ log: () => {} }).bindTo(loggerToken));

    expect(container.hasRegistration(loggerToken.token)).toBe(true);
  });

  it('should check current container and parent registrations', function () {
    // Parent container has a registration
    const parent = createAppContainer();
    parent.addRegistration(R.fromValue('parent-config').bindToKey('Config'));

    // Child scope does not have the registration
    const child = parent.createScope();
    child.addRegistration(R.fromValue('child-service').bindToKey('Service'));

    // Child should see parent's registration (checks parent as well)
    expect(child.hasRegistration('Config')).toBe(true);
    // Child should see its own registration
    expect(child.hasRegistration('Service')).toBe(true);
    // Parent should see its own registration
    expect(parent.hasRegistration('Config')).toBe(true);
  });

  it('should work with class-based registrations', function () {
    @register(bindTo('ILogger'))
    class Logger {}

    const container = createAppContainer();
    container.addRegistration(R.fromClass(Logger));

    expect(container.hasRegistration('ILogger')).toBe(true);
  });

  it('should be useful for conditional registration patterns', function () {
    const container = createAppContainer();

    // Register a base service
    container.addRegistration(R.fromValue('base-service').bindToKey('BaseService'));

    // Conditionally register an extension only if base exists
    if (container.hasRegistration('BaseService')) {
      container.addRegistration(R.fromValue('extension-service').bindToKey('ExtensionService'));
    }

    expect(container.hasRegistration('BaseService')).toBe(true);
    expect(container.hasRegistration('ExtensionService')).toBe(true);
  });
});

Dispose

Sometimes you want to dispose container and all its scopes. For example, when you want to prevent memory leaks. Or you want to ensure that nobody can use container after it was disposed.

• container can be disposed
• when container is disposed then all scopes are disposed too
• when container is disposed then it unregisters all providers and remove all instances

import 'reflect-metadata';
import { Container, ContainerDisposedError, Registration as R, select } from 'ts-ioc-container';

/**
 * User Management Domain - Resource Cleanup
 *
 * When a scope ends (e.g., HTTP request completes), resources must be cleaned up:
 * - Database connections returned to pool
 * - File handles closed
 * - Temporary files deleted
 * - Cache entries cleared
 *
 * The container.dispose() method:
 * 1. Executes all onDispose hooks
 * 2. Clears all instances and registrations
 * 3. Detaches from parent scope
 * 4. Prevents further resolution
 */

// Simulates a database connection that must be closed
class DatabaseConnection {
  isClosed = false;

  query(sql: string): string[] {
    if (this.isClosed) {
      throw new Error('Connection is closed');
    }
    return [`Result for: ${sql}`];
  }

  close(): void {
    this.isClosed = true;
  }
}

describe('Disposing', function () {
  it('should dispose container and prevent further usage', function () {
    const appContainer = new Container({ tags: ['application'] }).addRegistration(
      R.fromClass(DatabaseConnection).bindTo('IDatabase'),
    );

    // Create a request scope with a database connection
    const requestScope = appContainer.createScope({ tags: ['request'] });
    const connection = requestScope.resolve<DatabaseConnection>('IDatabase');

    // Connection works normally
    expect(connection.query('SELECT * FROM users')).toEqual(['Result for: SELECT * FROM users']);

    // Request ends - dispose the scope
    requestScope.dispose();

    // Scope is now unusable
    expect(() => requestScope.resolve('IDatabase')).toThrow(ContainerDisposedError);

    // All instances are cleared
    expect(select.instances().resolve(requestScope).length).toBe(0);

    // Application container is still functional
    expect(appContainer.resolve<DatabaseConnection>('IDatabase')).toBeDefined();
  });

  it('should clean up request-scoped resources on request end', function () {
    const appContainer = new Container({ tags: ['application'] }).addRegistration(
      R.fromClass(DatabaseConnection).bindTo('IDatabase'),
    );

    // Simulate Express.js request lifecycle
    function handleRequest(): { connection: DatabaseConnection; scope: Container } {
      const requestScope = appContainer.createScope({ tags: ['request'] }) as Container;
      const connection = requestScope.resolve<DatabaseConnection>('IDatabase');

      // Do some work...
      connection.query('INSERT INTO sessions VALUES (...)');

      return { connection, scope: requestScope };
    }

    // Request 1
    const request1 = handleRequest();
    expect(request1.connection.isClosed).toBe(false);

    // Request 1 ends - in Express, this would be in res.on('finish')
    request1.connection.close();
    request1.scope.dispose();

    // Request 2 gets a fresh connection
    const request2 = handleRequest();
    expect(request2.connection.isClosed).toBe(false);
    expect(request2.connection).not.toBe(request1.connection);

    // Cleanup
    request2.connection.close();
    request2.scope.dispose();
  });
});

Lazy

Sometimes you want to create dependency only when somebody want to invoke it's method or property. This is what lazy is for.

import 'reflect-metadata';
import { Container, inject, register, Registration as R, select as s, singleton } from 'ts-ioc-container';

/**
 * User Management Domain - Lazy Loading
 *
 * Some services are expensive to initialize:
 * - EmailNotifier: Establishes SMTP connection
 * - ReportGenerator: Loads templates, initializes PDF engine
 * - ExternalApiClient: Authenticates with third-party service
 *
 * Lazy loading defers instantiation until first use.
 * This improves startup time and avoids initializing unused services.
 *
 * Use cases:
 * - Services used only in specific code paths (error notification)
 * - Optional features that may not be triggered
 * - Breaking circular dependencies
 */
describe('lazy provider', () => {
  // Tracks whether SMTP connection was established
  @register(singleton())
  class SmtpConnectionStatus {
    isConnected = false;

    connect() {
      this.isConnected = true;
    }
  }

  // EmailNotifier is expensive - establishes SMTP connection on construction
  class EmailNotifier {
    constructor(@inject('SmtpConnectionStatus') private smtp: SmtpConnectionStatus) {
      // Simulate expensive SMTP connection
      this.smtp.connect();
    }

    sendPasswordReset(email: string): string {
      return `Password reset sent to ${email}`;
    }
  }

  // AuthService might need to send password reset emails
  // But most login requests don't need email (only password reset does)
  class AuthService {
    constructor(@inject(s.token('EmailNotifier').lazy()) public emailNotifier: EmailNotifier) {}

    login(email: string, password: string): boolean {
      // Most requests just validate credentials - no email needed
      return email === '[email protected]' && password === 'secret';
    }

    requestPasswordReset(email: string): string {
      // Only here do we actually need the EmailNotifier
      return this.emailNotifier.sendPasswordReset(email);
    }
  }

  function createContainer() {
    const container = new Container();
    container.addRegistration(R.fromClass(SmtpConnectionStatus)).addRegistration(R.fromClass(EmailNotifier));
    return container;
  }

  it('should not connect to SMTP until email is actually needed', () => {
    const container = createContainer();

    // AuthService is created, but EmailNotifier is NOT instantiated yet
    container.resolve(AuthService);
    const smtp = container.resolve<SmtpConnectionStatus>('SmtpConnectionStatus');

    // SMTP connection was NOT established - lazy loading deferred it
    expect(smtp.isConnected).toBe(false);
  });

  it('should connect to SMTP only when sending email', () => {
    const container = createContainer();

    const authService = container.resolve(AuthService);
    const smtp = container.resolve<SmtpConnectionStatus>('SmtpConnectionStatus');

    // Trigger password reset - this actually uses EmailNotifier
    const result = authService.requestPasswordReset('[email protected]');

    // Now SMTP connection was established
    expect(result).toBe('Password reset sent to [email protected]');
    expect(smtp.isConnected).toBe(true);
  });

  it('should only create one instance even with multiple method calls', () => {
    const container = createContainer();

    const authService = container.resolve(AuthService);

    // Multiple password resets
    authService.requestPasswordReset('[email protected]');
    authService.requestPasswordReset('[email protected]');

    // Only one EmailNotifier instance was created
    const emailNotifiers = Array.from(container.getInstances()).filter((x) => x instanceof EmailNotifier);
    expect(emailNotifiers.length).toBe(1);
  });

  it('should trigger instantiation when accessing property on lazy object', () => {
    const container = createContainer();

    const authService = container.resolve(AuthService);
    const smtp = container.resolve<SmtpConnectionStatus>('SmtpConnectionStatus');

    // Just getting the proxy doesn't trigger instantiation
    const notifier = authService.emailNotifier;
    expect(notifier).toBeDefined();
    expect(smtp.isConnected).toBe(false); // Still lazy!

    // Accessing a property ON the lazy object triggers instantiation
    const method = notifier.sendPasswordReset;
    expect(method).toBeDefined();
    expect(smtp.isConnected).toBe(true); // Now instantiated!
  });
});

Lazy with registerPipe

The lazy() registerPipe can be used in two ways: with the @register decorator or directly on the Provider pipe. This allows you to defer expensive service initialization until first access.

Use cases:

• Defer expensive initialization (database connections, SMTP, external APIs)
• Conditional features that may not be used
• Breaking circular dependencies
• Memory optimization for optional services

Two approaches:

1. With @register decorator: Use lazy() as a registerPipe in the decorator
2. With Provider pipe: Use Provider.fromClass().pipe(lazy()) directly

import 'reflect-metadata';
import { bindTo, Container, inject, lazy, Provider, register, Registration as R, singleton } from 'ts-ioc-container';

/**
 * Lazy Loading with registerPipe
 *
 * The lazy() registerPipe can be used in two ways:
 * 1. With @register decorator - lazy()
 * 2. Directly on provider - provider.lazy()
 *
 * Both approaches defer instantiation until first access,
 * improving startup time and memory usage.
 */
describe('lazy registerPipe', () => {
  // Track initialization for testing
  const initLog: string[] = [];

  beforeEach(() => {
    initLog.length = 0;
  });

  /**
   * Example 1: Using lazy() with @register decorator
   *
   * The lazy() registerPipe defers service instantiation until first use.
   * Perfect for expensive services that may not always be needed.
   */
  describe('with @register decorator', () => {
    // Database connection pool - expensive to initialize
    @register(bindTo('DatabasePool'), singleton())
    class DatabasePool {
      constructor() {
        initLog.push('DatabasePool initialized');
      }

      query(sql: string): string[] {
        return [`Results for: ${sql}`];
      }
    }

    // Analytics service - expensive, but only used occasionally
    @register(bindTo('AnalyticsService'), lazy(), singleton())
    class AnalyticsService {
      constructor(@inject('DatabasePool') private db: DatabasePool) {
        initLog.push('AnalyticsService initialized');
      }

      trackEvent(event: string): void {
        this.db.query(`INSERT INTO events VALUES ('${event}')`);
      }

      generateReport(): string {
        return 'Analytics Report';
      }
    }

    // Application service - always used
    class AppService {
      constructor(@inject('AnalyticsService') public analytics: AnalyticsService) {
        initLog.push('AppService initialized');
      }

      handleRequest(path: string): void {
        // Most requests don't need analytics
        if (path.includes('/admin')) {
          // Only admin requests use analytics
          this.analytics.trackEvent(`Admin access: ${path}`);
        }
      }
    }

    it('should defer AnalyticsService initialization until first access', () => {
      const container = new Container()
        .addRegistration(R.fromClass(DatabasePool))
        .addRegistration(R.fromClass(AnalyticsService))
        .addRegistration(R.fromClass(AppService));

      // Resolve AppService
      const app = container.resolve<AppService>(AppService);

      // AppService is initialized, but AnalyticsService is NOT (it's lazy)
      // DatabasePool is also not initialized because AnalyticsService hasn't been accessed
      expect(initLog).toEqual(['AppService initialized']);

      // Handle non-admin request - analytics not used
      app.handleRequest('/api/users');
      expect(initLog).toEqual(['AppService initialized']);
    });

    it('should initialize lazy service when first accessed', () => {
      const container = new Container()
        .addRegistration(R.fromClass(DatabasePool))
        .addRegistration(R.fromClass(AnalyticsService))
        .addRegistration(R.fromClass(AppService));

      const app = container.resolve<AppService>(AppService);

      // Handle admin request - now analytics IS used
      app.handleRequest('/admin/dashboard');

      // AnalyticsService was initialized on first access (DatabasePool too, as a dependency)
      expect(initLog).toEqual(['AppService initialized', 'DatabasePool initialized', 'AnalyticsService initialized']);
    });

    it('should create only one instance even with multiple accesses', () => {
      const container = new Container()
        .addRegistration(R.fromClass(DatabasePool))
        .addRegistration(R.fromClass(AnalyticsService))
        .addRegistration(R.fromClass(AppService));

      const app = container.resolve<AppService>(AppService);

      // Access analytics multiple times
      app.handleRequest('/admin/dashboard');
      app.analytics.generateReport();
      app.analytics.trackEvent('test');

      // AnalyticsService initialized only once (singleton + lazy)
      const analyticsCount = initLog.filter((msg) => msg === 'AnalyticsService initialized').length;
      expect(analyticsCount).toBe(1);
    });
  });

  /**
   * Example 2: Using lazy() directly on provider
   *
   * For manual registration, call .lazy() on the provider pipe.
   * This gives fine-grained control over lazy loading per dependency.
   */
  describe('with pure provider', () => {
    // Email service - expensive SMTP connection
    class EmailService {
      constructor() {
        initLog.push('EmailService initialized - SMTP connected');
      }

      send(to: string, subject: string): string {
        return `Email sent to ${to}: ${subject}`;
      }
    }

    // SMS service - expensive gateway connection
    class SmsService {
      constructor() {
        initLog.push('SmsService initialized - Gateway connected');
      }

      send(to: string, message: string): string {
        return `SMS sent to ${to}: ${message}`;
      }
    }

    // Notification service - uses email and SMS, but maybe not both
    class NotificationService {
      constructor(
        @inject('EmailService') public email: EmailService,
        @inject('SmsService') public sms: SmsService,
      ) {
        initLog.push('NotificationService initialized');
      }

      notifyByEmail(user: string, message: string): string {
        return this.email.send(user, message);
      }

      notifyBySms(phone: string, message: string): string {
        return this.sms.send(phone, message);
      }
    }

    it('should allow selective lazy loading - email lazy, SMS eager', () => {
      const container = new Container()
        // EmailService is lazy - won't connect to SMTP until used
        .addRegistration(
          R.fromClass(EmailService)
            .bindToKey('EmailService')
            .pipe(singleton(), (p) => p.lazy()),
        )
        // SmsService is eager - connects to gateway immediately
        .addRegistration(R.fromClass(SmsService).bindToKey('SmsService').pipe(singleton()))
        .addRegistration(R.fromClass(NotificationService));

      // Resolve NotificationService
      const notifications = container.resolve<NotificationService>(NotificationService);

      // SmsService initialized immediately (eager)
      // EmailService NOT initialized yet (lazy)
      expect(initLog).toEqual(['SmsService initialized - Gateway connected', 'NotificationService initialized']);

      // Send SMS - already initialized
      notifications.notifyBySms('555-1234', 'Test');
      expect(initLog).toEqual(['SmsService initialized - Gateway connected', 'NotificationService initialized']);
    });

    it('should initialize lazy email service when first accessed', () => {
      const container = new Container()
        .addRegistration(
          R.fromClass(EmailService)
            .bindToKey('EmailService')
            .pipe(singleton(), (p) => p.lazy()),
        )
        .addRegistration(R.fromClass(SmsService).bindToKey('SmsService').pipe(singleton()))
        .addRegistration(R.fromClass(NotificationService));

      const notifications = container.resolve<NotificationService>(NotificationService);

      // Send email - NOW EmailService is initialized
      const result = notifications.notifyByEmail('[email protected]', 'Welcome!');

      expect(result).toBe('Email sent to [email protected]: Welcome!');
      expect(initLog).toContain('EmailService initialized - SMTP connected');
    });

    it('should work with multiple lazy providers', () => {
      const container = new Container()
        // Both services are lazy
        .addRegistration(
          R.fromClass(EmailService)
            .bindToKey('EmailService')
            .pipe(singleton(), (p) => p.lazy()),
        )
        .addRegistration(
          R.fromClass(SmsService)
            .bindToKey('SmsService')
            .pipe(singleton(), (p) => p.lazy()),
        )
        .addRegistration(R.fromClass(NotificationService));

      const notifications = container.resolve<NotificationService>(NotificationService);

      // Neither service initialized yet
      expect(initLog).toEqual(['NotificationService initialized']);

      // Use SMS - only SMS initialized
      notifications.notifyBySms('555-1234', 'Test');
      expect(initLog).toEqual(['NotificationService initialized', 'SmsService initialized - Gateway connected']);

      // Use Email - now Email initialized
      notifications.notifyByEmail('[email protected]', 'Test');
      expect(initLog).toEqual([
        'NotificationService initialized',
        'SmsService initialized - Gateway connected',
        'EmailService initialized - SMTP connected',
      ]);
    });
  });

  /**
   * Example 3: Pure Provider usage (without Registration)
   *
   * Use Provider.fromClass() directly with lazy() for maximum flexibility.
   */
  describe('with pure Provider', () => {
    class CacheService {
      constructor() {
        initLog.push('CacheService initialized - Redis connected');
      }

      get(key: string): string | null {
        return `cached:${key}`;
      }
    }

    class ApiService {
      constructor(@inject('CacheService') private cache: CacheService) {
        initLog.push('ApiService initialized');
      }

      fetchData(id: string): string {
        const cached = this.cache.get(id);
        return cached || `fresh:${id}`;
      }
    }

    it('should use Provider.fromClass with lazy() helper', () => {
      // Create pure provider with lazy loading
      const cacheProvider = Provider.fromClass(CacheService).pipe(lazy(), singleton());

      const container = new Container();
      container.register('CacheService', cacheProvider);
      container.addRegistration(R.fromClass(ApiService));

      const api = container.resolve<ApiService>(ApiService);

      // CacheService not initialized yet (lazy)
      expect(initLog).toEqual(['ApiService initialized']);

      // Access cache - NOW it's initialized
      api.fetchData('user:1');
      expect(initLog).toContain('CacheService initialized - Redis connected');
    });

    it('should allow importing lazy as named export', () => {
      // Demonstrate that lazy() is imported from the library
      const cacheProvider = Provider.fromClass(CacheService).pipe(lazy());

      const container = new Container();
      container.register('CacheService', cacheProvider);

      const cache = container.resolve<CacheService>('CacheService');

      // Not initialized until accessed
      expect(initLog).toEqual([]);
      cache.get('test');
      expect(initLog).toEqual(['CacheService initialized - Redis connected']);
    });
  });

  /**
   * Example 4: Combining lazy with other pipes
   *
   * lazy() works seamlessly with other provider transformations.
   */
  describe('combining with other pipes', () => {
    class ConfigService {
      constructor(
        public apiUrl: string,
        public timeout: number,
      ) {
        initLog.push(`ConfigService initialized with ${apiUrl}`);
      }
    }

    it('should combine lazy with args and singleton', () => {
      const container = new Container().addRegistration(
        R.fromClass(ConfigService)
          .bindToKey('Config')
          .pipe(
            (p) => p.setArgs(() => ['https://api.example.com', 5000]),
            (p) => p.lazy(),
          )
          .pipe(singleton()),
      );

      // Config not initialized yet
      expect(initLog).toEqual([]);

      // Resolve - still not initialized (lazy)
      const config1 = container.resolve<ConfigService>('Config');
      expect(initLog).toEqual([]);

      // Access property - NOW initialized
      const url = config1.apiUrl;
      expect(url).toBe('https://api.example.com');
      expect(initLog).toEqual(['ConfigService initialized with https://api.example.com']);

      // Resolve again - same instance (singleton)
      const config2 = container.resolve<ConfigService>('Config');
      expect(config2).toBe(config1);
      expect(initLog.length).toBe(1); // Still only one initialization
    });
  });

  /**
   * Example 5: Real-world use case - Resource Management
   *
   * Lazy loading is ideal for:
   * - Database connections
   * - File handles
   * - External API clients
   * - Report generators
   */
  describe('real-world example - feature flags', () => {
    class FeatureFlagService {
      constructor() {
        initLog.push('FeatureFlagService initialized');
      }

      isEnabled(feature: string): boolean {
        return feature === 'premium';
      }
    }

    @register(bindTo('PremiumFeature'), lazy(), singleton())
    class PremiumFeature {
      constructor() {
        initLog.push('PremiumFeature initialized - expensive operation');
      }

      execute(): string {
        return 'Premium feature executed';
      }
    }

    class Application {
      constructor(
        @inject('FeatureFlagService') private flags: FeatureFlagService,
        @inject('PremiumFeature') private premium: PremiumFeature,
      ) {
        initLog.push('Application initialized');
      }

      handleRequest(feature: string): string {
        if (this.flags.isEnabled(feature)) {
          return this.premium.execute();
        }
        return 'Standard feature';
      }
    }

    it('should not initialize premium features for standard users', () => {
      const container = new Container()
        .addRegistration(R.fromClass(FeatureFlagService).bindToKey('FeatureFlagService').pipe(singleton()))
        .addRegistration(R.fromClass(PremiumFeature))
        .addRegistration(R.fromClass(Application));

      const app = container.resolve<Application>(Application);

      // Standard request - premium feature not initialized
      const result = app.handleRequest('standard');
      expect(result).toBe('Standard feature');
      expect(initLog).not.toContain('PremiumFeature initialized - expensive operation');
    });

    it('should initialize premium features only for premium users', () => {
      const container = new Container()
        .addRegistration(R.fromClass(FeatureFlagService).bindToKey('FeatureFlagService').pipe(singleton()))
        .addRegistration(R.fromClass(PremiumFeature))
        .addRegistration(R.fromClass(Application));

      const app = container.resolve<Application>(Application);

      // Premium request - NOW premium feature is initialized
      const result = app.handleRequest('premium');
      expect(result).toBe('Premium feature executed');
      expect(initLog).toContain('PremiumFeature initialized - expensive operation');
    });
  });
});

Injector

IInjector is used to describe how dependencies should be injected to constructor.

• MetadataInjector - injects dependencies using @inject decorator
• ProxyInjector - injects dependencies as dictionary Record<string, unknown>
• SimpleInjector - just passes container to constructor with others arguments

Metadata

This type of injector uses @inject decorator to mark where dependencies should be injected. It's bases on reflect-metadata package. That's why I call it MetadataInjector. Also you can inject property.

import { Container, inject, Registration as R } from 'ts-ioc-container';

/**
 * User Management Domain - Metadata Injection
 *
 * The MetadataInjector (default) uses TypeScript decorators and reflect-metadata
 * to automatically inject dependencies into constructor parameters.
 *
 * How it works:
 * 1. @inject('key') decorator marks a parameter for injection
 * 2. Container reads metadata at resolution time
 * 3. Dependencies are resolved and passed to constructor
 *
 * This is the most common pattern in Angular, NestJS, and similar frameworks.
 * Requires: "experimentalDecorators" and "emitDecoratorMetadata" in tsconfig.
 */

class Logger {
  name = 'Logger';
}

class App {
  // @inject tells the container which dependency to resolve for this parameter
  constructor(@inject('ILogger') private logger: Logger) {}

  // Alternative: inject via function for dynamic resolution
  // constructor(@inject((container, ...args) => container.resolve('ILogger', ...args)) private logger: ILogger) {}

  getLoggerName(): string {
    return this.logger.name;
  }
}

describe('Metadata Injector', function () {
  it('should inject dependencies using @inject decorator', function () {
    const container = new Container({ tags: ['application'] }).addRegistration(
      R.fromClass(Logger).bindToKey('ILogger'),
    );

    // Container reads @inject metadata and resolves 'ILogger' for the logger parameter
    const app = container.resolve(App);

    expect(app.getLoggerName()).toBe('Logger');
  });
});

Simple

This type of injector just passes container to constructor with others arguments.

import { Container, type IContainer, Registration as R, SimpleInjector } from 'ts-ioc-container';

/**
 * Command Pattern - Simple Injector
 *
 * The SimpleInjector passes the container itself as the first argument to the constructor.
 * This is useful for:
 * - Service Locators (like Command Dispatchers or Routers)
 * - Factory classes that need to resolve dependencies dynamically
 * - Legacy code migration where passing the container is common
 *
 * In this example, a CommandDispatcher uses the container to dynamically
 * resolve the correct handler for each command type.
 */

interface ICommand {
  type: string;
}

interface ICommandHandler {
  handle(command: ICommand): string;
}

class CreateUserCommand implements ICommand {
  readonly type = 'CreateUser';
  constructor(readonly username: string) {}
}

class CreateUserHandler implements ICommandHandler {
  handle(command: CreateUserCommand): string {
    return `User ${command.username} created`;
  }
}

describe('SimpleInjector', function () {
  it('should inject container to allow dynamic resolution (Service Locator pattern)', function () {
    // Dispatcher needs the container to find handlers dynamically based on command type
    class CommandDispatcher {
      constructor(private container: IContainer) {}

      dispatch(command: ICommand): string {
        // Dynamically resolve handler: "Handler" + "CreateUser"
        const handlerKey = `Handler${command.type}`;
        const handler = this.container.resolve<ICommandHandler>(handlerKey);
        return handler.handle(command);
      }
    }

    const container = new Container({ injector: new SimpleInjector() })
      .addRegistration(R.fromClass(CommandDispatcher).bindToKey('Dispatcher'))
      .addRegistration(R.fromClass(CreateUserHandler).bindToKey('HandlerCreateUser'));

    const dispatcher = container.resolve<CommandDispatcher>('Dispatcher');
    const result = dispatcher.dispatch(new CreateUserCommand('alice'));

    expect(result).toBe('User alice created');
  });

  it('should pass additional arguments alongside the container', function () {
    // Factory that creates widgets with a specific theme
    class WidgetFactory {
      constructor(
        private container: IContainer,
        private theme: string, // Passed as argument during resolve
      ) {}

      createWidget(name: string): string {
        return `Widget ${name} with ${this.theme} theme (Container available: ${!!this.container})`;
      }
    }

    const container = new Container({ injector: new SimpleInjector() }).addRegistration(
      R.fromClass(WidgetFactory).bindToKey('WidgetFactory'),
    );

    // Pass "dark" as the theme argument
    const factory = container.resolve<WidgetFactory>('WidgetFactory', { args: ['dark'] });

    expect(factory.createWidget('Button')).toBe('Widget Button with dark theme (Container available: true)');
  });
});

Proxy

This type of injector injects dependencies as dictionary Record<string, unknown>.

import { Container, ProxyInjector, Registration as R } from 'ts-ioc-container';

/**
 * Clean Architecture - Proxy Injector
 *
 * The ProxyInjector injects dependencies as a single object (props/options pattern).
 * This is popular in modern JavaScript/TypeScript (like React props or destructuring).
 *
 * Advantages:
 * - Named parameters are more readable than positional arguments
 * - Order of arguments doesn't matter
 * - Easy to add/remove dependencies without breaking inheritance chains
 * - Works well with "Clean Architecture" adapters
 */

describe('ProxyInjector', function () {
  it('should inject dependencies as a props object', function () {
    class Logger {
      log(msg: string) {
        return `Logged: ${msg}`;
      }
    }

    // Dependencies defined as an interface
    interface UserControllerDeps {
      logger: Logger;
      prefix: string;
    }

    // Controller receives all dependencies in a single object
    class UserController {
      private logger: Logger;
      private prefix: string;

      constructor({ logger, prefix }: UserControllerDeps) {
        this.logger = logger;
        this.prefix = prefix;
      }

      createUser(name: string): string {
        return this.logger.log(`${this.prefix} ${name}`);
      }
    }

    const container = new Container({ injector: new ProxyInjector() })
      .addRegistration(R.fromClass(Logger).bindToKey('logger'))
      .addRegistration(R.fromValue('USER:').bindToKey('prefix'))
      .addRegistration(R.fromClass(UserController).bindToKey('UserController'));

    const controller = container.resolve<UserController>('UserController');

    expect(controller.createUser('bob')).toBe('Logged: USER: bob');
  });

  it('should support mixing injected dependencies with runtime arguments', function () {
    class Database {}

    interface ReportGeneratorDeps {
      database: Database;
      format: string; // Runtime argument
    }

    class ReportGenerator {
      constructor(public deps: ReportGeneratorDeps) {}

      generate(): string {
        return `Report in ${this.deps.format}`;
      }
    }

    const container = new Container({ injector: new ProxyInjector() })
      .addRegistration(R.fromClass(Database).bindToKey('database'))
      .addRegistration(R.fromClass(ReportGenerator).bindToKey('ReportGenerator'));

    // "format" is passed at resolution time
    const generator = container.resolve<ReportGenerator>('ReportGenerator', {
      args: [{ format: 'PDF' }],
    });

    expect(generator.deps.database).toBeInstanceOf(Database);
    expect(generator.generate()).toBe('Report in PDF');
  });

  it('should resolve array dependencies by alias (convention over configuration)', function () {
    // If a property is named "loggersArray", it looks for alias "loggersArray"
    // and resolves it as an array of all matches.

    class FileLogger {}
    class ConsoleLogger {}

    interface AppDeps {
      loggersArray: any[]; // Injected as array of all loggers
    }

    class App {
      constructor(public deps: AppDeps) {}
    }

    const container = new Container({ injector: new ProxyInjector() });

    // Mocking the behavior for this specific test as ProxyInjector uses resolveByAlias
    // which delegates to the container.
    // In a real scenario, you'd register multiple loggers with the same alias.
    const mockLoggers = [new FileLogger(), new ConsoleLogger()];

    container.resolveByAlias = jest.fn().mockReturnValue(mockLoggers);

    const app = container.resolve(App);

    expect(app.deps.loggersArray).toBe(mockLoggers);
    expect(container.resolveByAlias).toHaveBeenCalledWith('loggersArray');
  });
});

Provider

Provider is dependency factory which creates dependency.

• Provider.fromClass(Logger)
• Provider.fromValue(logger)
• new Provider((container, ...args) => container.resolve(Logger, {args}))

import {
  args,
  argsFn,
  bindTo,
  Container,
  lazy,
  Provider,
  register,
  Registration as R,
  scopeAccess,
  singleton,
} from 'ts-ioc-container';

/**
 * Data Processing Pipeline - Provider Patterns
 *
 * Providers are the recipes for creating objects. This suite demonstrates
 * how to customize object creation for a Data Processing Pipeline.
 *
 * Scenarios:
 * - FileProcessor: Created as a class instance
 * - Config: Created from a simple value object
 * - BatchProcessor: Singleton to coordinate across the app
 * - StreamProcessor: Lazy loaded only when needed
 */

class Logger {}

describe('Provider', () => {
  it('can be registered as a function (Factory Pattern)', () => {
    // dynamic factory
    const container = new Container().register('ILogger', new Provider(() => new Logger()));
    expect(container.resolve('ILogger')).not.toBe(container.resolve('ILogger'));
  });

  it('can be registered as a value (Config Pattern)', () => {
    // constant value
    const config = { maxRetries: 3 };
    const container = new Container().register('Config', Provider.fromValue(config));
    expect(container.resolve('Config')).toBe(config);
  });

  it('can be registered as a class (Standard Pattern)', () => {
    const container = new Container().register('ILogger', Provider.fromClass(Logger));
    expect(container.resolve('ILogger')).toBeInstanceOf(Logger);
  });

  it('can be featured by fp method (Singleton Pattern)', () => {
    // Pipe "singleton()" to cache the instance
    const appContainer = new Container({ tags: ['application'] }).register(
      'SharedLogger',
      Provider.fromClass(Logger).pipe(singleton()),
    );
    expect(appContainer.resolve('SharedLogger')).toBe(appContainer.resolve('SharedLogger'));
  });

  it('can be created from a dependency key (Alias/Redirect Pattern)', () => {
    // "LoggerAlias" redirects to "ILogger"
    const container = new Container()
      .register('ILogger', Provider.fromClass(Logger))
      .register('LoggerAlias', Provider.fromKey('ILogger'));

    const logger = container.resolve('LoggerAlias');
    expect(logger).toBeInstanceOf(Logger);
  });

  it('supports lazy resolution (Performance Optimization)', () => {
    // Logger is not created until accessed
    const container = new Container().register('ILogger', Provider.fromClass(Logger));
    const lazyLogger = container.resolve('ILogger', { lazy: true });

    // It's a proxy, not the real instance yet
    expect(typeof lazyLogger).toBe('object');
    // Accessing it would trigger creation
  });

  it('supports args decorator for providing extra arguments', () => {
    class FileService {
      constructor(readonly basePath: string) {}
    }

    const container = new Container().register('FileService', Provider.fromClass(FileService).pipe(args('/var/data')));

    const service = container.resolve<FileService>('FileService');
    expect(service.basePath).toBe('/var/data');
  });

  it('supports argsFn decorator for dynamic arguments', () => {
    class Database {
      constructor(readonly connectionString: string) {}
    }

    const container = new Container().register('DbPath', Provider.fromValue('localhost:5432')).register(
      'Database',
      Provider.fromClass(Database).pipe(
        // Dynamically resolve connection string at creation time
        argsFn((scope) => [`postgres://${scope.resolve('DbPath')}`]),
      ),
    );

    const db = container.resolve<Database>('Database');
    expect(db.connectionString).toBe('postgres://localhost:5432');
  });

  it('supports visibility control (Security Pattern)', () => {
    // AdminService only visible in admin scope
    class AdminService {}

    const appContainer = new Container({ tags: ['application'] }).register(
      'AdminService',
      Provider.fromClass(AdminService).pipe(scopeAccess(({ invocationScope }) => invocationScope.hasTag('admin'))),
    );

    const adminScope = appContainer.createScope({ tags: ['admin'] });
    const publicScope = appContainer.createScope({ tags: ['public'] });

    expect(() => adminScope.resolve('AdminService')).not.toThrow();
    expect(() => publicScope.resolve('AdminService')).toThrow();
  });

  it('allows to register lazy provider via decorator', () => {
    let created = false;

    @register(bindTo('HeavyService'), lazy())
    class HeavyService {
      constructor() {
        created = true;
      }
      doWork() {}
    }

    const container = new Container().addRegistration(R.fromClass(HeavyService));
    const service = container.resolve<HeavyService>('HeavyService');

    expect(created).toBe(false); // Not created yet
    service.doWork(); // Access triggers creation
    expect(created).toBe(true);
  });
});

Singleton

Sometimes you need to create only one instance of dependency per scope. For example, you want to create only one logger per scope.

• Singleton provider creates only one instance in every scope where it's resolved.
• NOTICE: if you create a scope 'A' of container 'root' then Logger of A !== Logger of root.

import 'reflect-metadata';
import { bindTo, Container, register, Registration as R, singleton } from 'ts-ioc-container';

/**
 * User Management Domain - Singleton Pattern
 *
 * Singletons are services that should only have one instance per scope.
 * Common examples:
 * - PasswordHasher: Expensive to initialize (loads crypto config)
 * - DatabasePool: Connection pool shared across requests
 * - ConfigService: Application configuration loaded once
 *
 * Note: "singleton" in ts-ioc-container means "one instance per scope",
 * not "one instance globally". Each scope gets its own singleton instance.
 */

// PasswordHasher is expensive to create - should be singleton
@register(bindTo('IPasswordHasher'), singleton())
class PasswordHasher {
  private readonly salt: string;

  constructor() {
    // Simulate expensive initialization (loading crypto config, etc.)
    this.salt = 'random_salt_' + Math.random().toString(36);
  }

  hash(password: string): string {
    return `hashed_${password}_${this.salt}`;
  }

  verify(password: string, hash: string): boolean {
    return this.hash(password) === hash;
  }
}

describe('Singleton', function () {
  function createAppContainer() {
    return new Container({ tags: ['application'] });
  }

  it('should resolve the same PasswordHasher for every request in same scope', function () {
    const appContainer = createAppContainer().addRegistration(R.fromClass(PasswordHasher));

    // Multiple resolves return the same instance
    const hasher1 = appContainer.resolve<PasswordHasher>('IPasswordHasher');
    const hasher2 = appContainer.resolve<PasswordHasher>('IPasswordHasher');

    expect(hasher1).toBe(hasher2);
    expect(hasher1.hash('password')).toBe(hasher2.hash('password'));
  });

  it('should create different singleton per request scope', function () {
    // Application-level singleton
    const appContainer = createAppContainer().addRegistration(R.fromClass(PasswordHasher));

    // Each request scope gets its own singleton instance
    // This is useful when you want per-request caching
    const request1 = appContainer.createScope({ tags: ['request'] });
    const request2 = appContainer.createScope({ tags: ['request'] });

    const appHasher = appContainer.resolve<PasswordHasher>('IPasswordHasher');
    const request1Hasher = request1.resolve<PasswordHasher>('IPasswordHasher');
    const request2Hasher = request2.resolve<PasswordHasher>('IPasswordHasher');

    // Each scope has its own instance
    expect(appHasher).not.toBe(request1Hasher);
    expect(request1Hasher).not.toBe(request2Hasher);
  });

  it('should maintain singleton within a scope', function () {
    const appContainer = createAppContainer().addRegistration(R.fromClass(PasswordHasher));
    const requestScope = appContainer.createScope({ tags: ['request'] });

    // Within the same scope, singleton is maintained
    const hasher1 = requestScope.resolve<PasswordHasher>('IPasswordHasher');
    const hasher2 = requestScope.resolve<PasswordHasher>('IPasswordHasher');

    expect(hasher1).toBe(hasher2);
  });
});

Arguments

Sometimes you want to bind some arguments to provider. This is what ArgsProvider is for.

• provider(args('someArgument'))
• provider(argsFn((container) => [container.resolve(Logger), 'someValue']))
• Provider.fromClass(Logger).pipe(args('someArgument'))
• NOTICE: args from this provider has higher priority than args from resolve method.

import {
  args,
  argsFn,
  bindTo,
  Container,
  inject,
  MultiCache,
  register,
  Registration as R,
  resolveByArgs,
  singleton,
  SingleToken,
} from 'ts-ioc-container';

/**
 * Advanced - Arguments Provider
 *
 * You can inject arguments into providers at registration time or resolution time.
 * This is powerful for:
 * - Configuration injection
 * - Factory patterns
 * - Generic classes (like Repositories) that need to know what they are managing
 */

describe('ArgsProvider', function () {
  function createContainer() {
    return new Container();
  }

  describe('Static Arguments', () => {
    it('can pass static arguments to constructor', function () {
      class FileLogger {
        constructor(public filename: string) {}
      }

      // Pre-configure the logger with a filename
      const root = createContainer().addRegistration(R.fromClass(FileLogger).pipe(args('/var/log/app.log')));

      // Resolve by class name (default key) to use the registered provider
      const logger = root.resolve<FileLogger>('FileLogger');
      expect(logger.filename).toBe('/var/log/app.log');
    });

    it('prioritizes provided args over resolve args', function () {
      class Logger {
        constructor(public context: string) {}
      }

      // 'FixedContext' wins over any runtime args
      const root = createContainer().addRegistration(R.fromClass(Logger).pipe(args('FixedContext')));

      // Even if we ask for 'RuntimeContext', we get 'FixedContext'
      // Resolve by class name to use the registered provider
      const logger = root.resolve<Logger>('Logger', { args: ['RuntimeContext'] });

      expect(logger.context).toBe('FixedContext');
    });
  });

  describe('Dynamic Arguments (Factory)', () => {
    it('can resolve arguments dynamically from container', function () {
      class Config {
        env = 'production';
      }

      class Service {
        constructor(public env: string) {}
      }

      const root = createContainer()
        .addRegistration(R.fromClass(Config)) // Key: 'Config'
        .addRegistration(
          R.fromClass(Service).pipe(
            // Extract 'env' from Config service dynamically
            // Note: We resolve 'Config' by string key to get the registered instance (if it were singleton)
            argsFn((scope) => [scope.resolve<Config>('Config').env]),
          ),
        );

      const service = root.resolve<Service>('Service');
      expect(service.env).toBe('producti