TypeScript Dependency Injection Container

ts-ioc-container is a fast, lightweight TypeScript dependency injection container for applications that need more than basic constructor injection: scoped lifecycles, decorators, typed tokens, lazy dependencies, lifecycle hooks, provider pipelines, aliases, and custom injector strategies.

Advantages

• fast TypeScript dependency resolution
• lightweight and dependency-minimal
• clean API for classes, keys, tokens, aliases, and scopes
• no global container object; pass containers and scopes explicitly
• supports tagged application, request, transaction, page, and widget scopes
• decorator support with @register, @inject, and @hook — lifecycle hook keys are yours to name
• can inject properties
• can inject lazy dependencies
• composable provider and registration pipelines
• custom injectors, hooks, and provider behavior

Content

• Setup
• Environment support
• Quickstart
• Cheatsheet
• Container
  • Basic usage
  • Scope tags
  • Instances
  • Dispose
  • Lazy lazy
  • Lazy with registerPipe lazy()
• Injector
  • Metadata @inject
  • Mapping injected values
  • Simple
  • Proxy
• Provider provider
  • Singleton singleton
  • Auto resolve autoResolve
  • Arguments appendArgs appendArgsFn
  • Visibility visible
  • Alias asAlias
  • Decorator decorate
  • On resolve onResolve
• Registration @register
  • Token bindTo
  • Scope scope
  • Composing decorators createComposeClassDecorator
• Module
• Hook @hook
  • Hook domains ScopeHook InjectorHook ProviderHook
  • Construct hooks onConstructed
  • Scope disposal hooks scopeDisposed
  • 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
  }
}

Environment support

ts-ioc-container ships both CommonJS and ES module builds (selected automatically via the package exports map) plus TypeScript declarations, so it runs anywhere modern JavaScript does. The package is sideEffects-free, so bundlers tree-shake unused exports.

| Environment | Supported | Module format | Notes | | --- | :---: | --- | --- | | Node.js (ESM, import) | ✅ | ESM | Node.js 18+; resolved via the import condition. | | Node.js (CommonJS, require) | ✅ | CJS | Node.js 18+; resolved via the require condition. | | Browser / Web (via bundlers) | ✅ | ESM | webpack, Vite, Rollup, esbuild, Parcel; tree-shakeable. | | TypeScript | ✅ | CJS + ESM | Types shipped for both; needs experimentalDecorators for the metadata injector. | | Deno | ✅ | ESM | Use the npm:ts-ioc-container specifier. | | Bun | ✅ | CJS + ESM | Runs the native ESM/CJS builds directly. |

[!NOTE] The default MetadataInjector (and the @inject / @hook decorators) rely on reflect-metadata. It is declared as an optional peer dependency — install it and import it once at your entrypoint. SimpleInjector and ProxyInjector do not need it.

Quickstart

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

interface ILogger {
  log(message: string): void;
}

const ILoggerToken = new SingleToken<ILogger>('ILogger');

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

class App {
  constructor(@inject(by(ILoggerToken)) private logger: ILogger) {}
  start() {
    this.logger.log('hello');
  }
}

describe('Quickstart', function () {
  it('should resolve App with injected Logger', function () {
    const container = new Container({ tags: ['application'] }).addRegistration(R.fromClass(Logger));

    const app = container.resolve(App);
    app.start();

    expect(app).toBeInstanceOf(App);
  });
});

Cheatsheet

• Register class with key (preferred): @register(bindTo('Key')) class Service {} then container.addRegistration(R.fromClass(Service))
• Register value: R.fromValue(config).bindTo('Config')
• Register factory: R.fromFn(({ scope }) => createX(scope)).bindTo('X')
• Singleton: @register(singleton())
• Eager service: @register(autoResolve()) + container.useModule(new AutoResolveModule())
• 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(by(Token)) / @inject(by('Key')) / @inject(by(Logger)) — the argument is always one InjectFn, by(...) builds the usual one
• Custom inject function: @inject(({ scope, args }) => ...)
• Map an injected value: @inject(pipe(by('Key'), sanitize(), validate()))
• Property inject: @hook('onInit', injectProp(by('Key')))
• Name a decorator stack: const repository = (token) => createComposeClassDecorator(register(token, singleton()), addClassMeta('injection-token', () => token))

[!TIP] For classes, prefer the @register(bindTo('Key')) decorator over the fluent R.fromClass(Class).bindTo('Key') chain. The decorator co-locates the binding with the class and reads consistently with other registration pipes (scope, singleton, appendArgsFn, ...). Use the fluent bindTo chain only for R.fromValue(...) and R.fromFn(...) (which have no class to decorate) or for third-party classes you don't own.

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 { bindTo, Container, type IContainer, inject, register, Registration as R, select, by } 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
  @register(bindTo('IUserRepository'))
  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(by('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));

    // 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(by(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.

[!IMPORTANT] Scope creation is snapshot-like. Existing parent registrations are applied to the child scope when createScope() is called, and when a scope doesn't have a dependency it resolves from the parent container.

[!WARNING] Registrations added to a parent after a child scope has already been created are not automatically applied to that existing child. Create a new scope or add the registration to the child explicitly.

[!WARNING] Scope matching happens when a registration is applied to a container. Only registrations whose scope rules match that container are registered there.

import 'reflect-metadata';
import {
  bindTo,
  Container,
  DependencyNotFoundError,
  type IContainer,
  inject,
  register,
  Registration as R,
  scope,
  select,
  singleton,
  by,
} 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(by(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);
  });
});

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, by } 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(by(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(by(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(by(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);
  });
});

Dispose

Sometimes you want to dispose a container or scope. For example, when a request, page, widget, or other local lifecycle ends.

• container can be disposed
• when container is disposed then it runs its onScopeDisposed hooks, unregisters its providers, removes its local instances, and detaches from its parent

[!IMPORTANT] Dispose is local to the container being disposed. Child scopes are not disposed automatically; dispose them explicitly when their own lifecycle ends.

import 'reflect-metadata';
import { bindTo, Container, ContainerDisposedError, register, 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 onScopeDisposed hooks
 * 2. Clears all instances and registrations
 * 3. Detaches from parent scope
 * 4. Prevents further resolution
 */

// Simulates a database connection that must be closed
@register(bindTo('IDatabase'))
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));

    // 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));

    // 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.

• Lazy class instances are wrapped in a JavaScript Proxy; the real class instance is created on first property or method access.

[!IMPORTANT] lazy is designed only for class instances resolved from class providers.

[!WARNING] Do not use lazy for primitive values, plain values, functions, or non-class provider results.

import 'reflect-metadata';
import { Container, inject, register, Registration as R, select as s, singleton, by } 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(by('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(by(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 class instance 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 {
  appendArgs,
  arg,
  bindTo,
  Container,
  inject,
  lazy,
  Provider,
  register,
  Registration as R,
  singleton,
  by,
} 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(by('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(by('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(by('EmailService')) public email: EmailService,
        @inject(by('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).pipe(singleton(), lazy()))
        // SmsService is eager - connects to gateway immediately
        .addRegistration(R.fromClass(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).pipe(singleton(), lazy()))
        .addRegistration(R.fromClass(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).pipe(singleton(), lazy()))
        .addRegistration(R.fromClass(SmsService).pipe(singleton(), 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(by('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).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).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', () => {
    @register(bindTo('Config'))
    class ConfigService {
      constructor(
        @inject(arg(0)) public apiUrl: string,
        @inject(arg(1)) 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).pipe(appendArgs('https://api.example.com', 5000), 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', () => {
    @register(singleton())
    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(by('FeatureFlagService')) private flags: FeatureFlagService,
        @inject(by('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))
        .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))
        .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.

@inject takes exactly one argument, an InjectFn: (options: ProviderOptions) => T. It is called with the resolution context of the class being constructed — the scope it is built in and the runtime args it is built with — and whatever it returns is injected. There is no other form, only functions which build one:

• by(target) — resolves a token, a DependencyKey or a class from the scope, forwarding the runtime args (see runtime args flow through tokens): @inject(by(LoggerToken)), @inject(by('Logger')), @inject(by(Logger)).
• arg(index) / args / argsFn(predicate) — pick from the runtime args.
• pipe(fn, ...mappers) — map what another InjectFn returns.
• Your own: @inject(({ scope }) => scope) injects the current scope, @inject(({ scope }) => Token.resolve(scope)) resolves a token without the args.

import { bindTo, Container, inject, register, Registration as R, by } 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(by('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.
 */

@register(bindTo('ILogger'))
class Logger {
  name = 'Logger';
}

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

  // Alternative: inject via function for dynamic resolution
  // constructor(@inject(by('ILogger')) 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));

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

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

Mapping injected values

An InjectFn is a function, so mapping the value it resolves is function composition — pipe(fn, ...mappers) (exported) runs each mapper on the previous result, left to right, and the value the last one returns is what reaches the constructor parameter:

@inject(pipe(by<Config>('Config'), takeApiUrl(), stripTrailingSlash(), requireHttps()))

A mapper is a plain (value) => value function, so mappers compose into named, reusable steps (selecting a member, sanitizing, validating) and each step's parameter type is inferred from the previous one. pipe(fn, ...mappers) is itself an InjectFn, so it goes wherever one does — @inject(...), a FunctionToken, or injectProp(pipe(by('Config'), takeApiUrl())).

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

/**
 * Mapping injected values
 *
 * `@inject` takes one `InjectFn`, so mapping what it resolves is composition:
 * `pipe(fn, ...mappers)` applies each mapper to the previous result, left to
 * right, and is itself an `InjectFn`. Mappers are plain functions, so they
 * compose into reusable, named steps.
 */

interface Config {
  apiUrl: string;
  retries: number;
}

// Reusable mappers, each returning a `(value) => value` function
const takeApiUrl = () => (config: Config) => config.apiUrl;
const stripTrailingSlash = () => (url: string) => url.replace(/\/$/, '');
const requireHttps = () => (url: string) => {
  if (!url.startsWith('https://')) {
    throw new Error(`Insecure api url: ${url}`);
  }
  return url;
};

describe('inject mappers', () => {
  it('should pipe the resolved dependency through every mapper', () => {
    class ApiClient {
      constructor(
        @inject(pipe(by<Config>('Config'), takeApiUrl(), stripTrailingSlash(), requireHttps()))
        readonly apiUrl: string,
      ) {}
    }

    const container = new Container().addRegistration(
      R.fromValue<Config>({ apiUrl: 'https://api.com/', retries: 3 }).bindToKey('Config'),
    );

    expect(container.resolve(ApiClient).apiUrl).toBe('https://api.com');
  });

  it('should throw from a mapper when the resolved value is not acceptable', () => {
    class ApiClient {
      constructor(
        @inject(pipe(by<Config>('Config'), takeApiUrl(), requireHttps()))
        readonly apiUrl: string,
      ) {}
    }

    const container = new Container().addRegistration(
      R.fromValue<Config>({ apiUrl: 'http://api.com', retries: 3 }).bindToKey('Config'),
    );

    expect(() => container.resolve(ApiClient)).toThrow('Insecure api url: http://api.com');
  });
});

Simple

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

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

@register(bindTo('HandlerCreateUser'))
class CreateUserHandler {
  handle(username: string): string {
    return `User ${username} created`;
  }
}

describe('SimpleInjector', function () {
  it('should inject container to allow dynamic resolution', function () {
    @register(bindTo('Dispatcher'))
    class CommandDispatcher {
      constructor(private container: IContainer) {}

      dispatch(type: string, payload: string): string {
        const handler = this.container.resolve<CreateUserHandler>(`Handler${type}`);
        return handler.handle(payload);
      }
    }

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

    const dispatcher = container.resolve<CommandDispatcher>('Dispatcher');

    expect(dispatcher.dispatch('CreateUser', 'alice')).toBe('User alice created');
  });

  it('should pass additional arguments alongside the container', function () {
    class WidgetFactory {
      constructor(
        private container: IContainer,
        private theme: string,
      ) {}

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

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

    const factory = container.resolve<WidgetFactory>('WidgetFactory', { args: ['dark'] });

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

Proxy

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

• args reserved keyword: accessing deps.args returns the raw args[] array passed at resolve time
• Alias convention: any property name containing "alias" (case-insensitive) is resolved via resolveByAlias instead of resolve

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

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

    class UserController {
      private logger: Logger;
      private prefix: string;

      constructor({ logger, prefix }: { logger: Logger; prefix: string }) {
        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))
      .addRegistration(R.fromValue('USER:').bindToKey('prefix'))
      .addRegistration(R.fromClass(UserController));

    expect(container.resolve<UserController>('UserController').createUser('bob')).toBe('Logged: USER: bob');
  });

  it('should expose runtime args through the reserved "args" property', function () {
    class ReportGenerator {
      format: string;

      constructor({ args }: { args: string[] }) {
        this.format = args[0];
      }

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

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

    const generator = container.resolve<ReportGenerator>('ReportGenerator', { args: ['PDF'] });

    expect(generator.generate()).toBe('Report in PDF');
  });
});

Provider

Provider is dependency factory which creates dependency.

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

import { arg, bindTo, Container, inject, lazy, Provider, register, Registration as R } 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)', () => {
    // Use ".singleton()" to cache the instance
    const appContainer = new Container({ tags: ['application'] }).register(
      'SharedLogger',
      Provider.fromClass(Logger).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(@inject(arg(0)) readonly basePath: string) {}
    }

    const container = new Container().register(
      'FileService',
      Provider.fromClass(FileService).addArgsFn(({ args = [] }) => [...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(@inject(arg(0)) readonly connectionString: string) {}
    }

    const container = new Container().register('DbPath', Provider.fromValue('localhost:5432')).register(
      'Database',
      // Dynamically resolve connection string at creation time
      Provider.fromClass(Database).addArgsFn(({ 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).addAccessRule(({ 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.

[!IMPORTANT] Singleton means one instance per scope. 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);
  });
});

Auto resolve

Some services are never injected anywhere - they subscribe to a queue, start a timer, or warm a cache as soon as their scope exists. Lazy resolution would never create them, because nothing asks for them.

• @register(autoResolve()) marks a provider as eager
• container.useModule(new AutoResolveModule()) enables eager resolution for every scope created afterwards
• container.autoResolve() resolves the eager providers of one container on demand

Both accept an optional AutoResolveOptions ({ args?: unknown[] }) whose args are forwarded to every eagerly resolved provider, exactly as resolve forwards them - so they reach @inject(arg(0)) parameters, scopeAccess rules and the singleton() cache key. new AutoResolveModule({ args }) applies the same args to every created scope; call scope.autoResolve({ args }) yourself when the value differs per scope.

[!IMPORTANT] autoResolve() on its own does nothing - the container has to opt in with AutoResolveModule. The container the module is applied to is not a created scope, so call container.autoResolve() explicitly to eagerly resolve its own providers.

Eager resolution goes through the provider unchanged, so singleton() still returns the eagerly created instance later, and providers which are not registered in the created scope (scope(...)) or deny access to it (scopeAccess(...)) are skipped.

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

/**
 * User Management Domain - Eager Services
 *
 * Some services are never injected anywhere: they subscribe to a queue, start a
 * timer, or warm a cache as soon as their scope exists. Nothing resolves them,
 * so lazy resolution would never create them at all.
 *
 * `autoResolve()` marks such a provider as eager, and `AutoResolveModule`
 * resolves every eager provider of a scope right after the scope is created.
 */

const auditTrail: string[] = [];
const openedLogs: string[] = [];

// Started for every request, even though no other class injects it
@register(bindTo('IRequestAuditor'), scope((s) => s.hasTag('request')), autoResolve(), singleton())
class RequestAuditor {
  constructor() {
    auditTrail.push('request started');
  }
}

// Eager too, but parameterized - the args come from whoever triggers eager resolution
@register(bindTo('IRequestLog'), scope((s) => s.hasTag('request')), autoResolve())
class RequestLog {
  constructor(@inject(arg(0)) readonly requestId: string = 'anonymous') {
    openedLogs.push(requestId);
  }
}

// Resolved on demand, the usual way
@register(bindTo('IUserRepository'), singleton())
class UserRepository {
  findById(id: string): string {
    return `user_${id}`;
  }
}

describe('Auto resolve', function () {
  function createAppContainer(options: { args?: unknown[] } = {}): IContainer {
    return new Container({ tags: ['application'] })
      .useModule(new AutoResolveModule(options))
      .addRegistration(R.fromClass(RequestAuditor))
      .addRegistration(R.fromClass(RequestLog))
      .addRegistration(R.fromClass(UserRepository));
  }

  beforeEach(() => {
    auditTrail.length = 0;
    openedLogs.length = 0;
  });

  it('should create eager services as soon as a scope is created', function () {
    const app = createAppContainer();

    // Nothing has been created yet - the application container is not a created scope
    expect(auditTrail).toEqual([]);

    app.createScope({ tags: ['request'] });
    app.createScope({ tags: ['request'] });

    // One auditor per request scope, without anybody resolving it
    expect(auditTrail).toEqual(['request started', 'request started']);
  });

  it('should reuse the eagerly created instance', function () {
    const requestScope = createAppContainer().createScope({ tags: ['request'] });

    const auditor = requestScope.resolve<RequestAuditor>('IRequestAuditor');

    expect(auditTrail).toEqual(['request started']);
    expect(requestScope.resolve<RequestAuditor>('IRequestAuditor')).toBe(auditor);
  });

  it('should treat resolve options as optional', function () {
    createAppContainer().createScope({ tags: ['request'] });

    expect(openedLogs).toEqual(['anonymous']);
  });

  it('should forward args to every eagerly resolved provider', function () {
    // The same args reach every scope the module creates...
    createAppContainer({ args: ['req-42'] }).createScope({ tags: ['request'] });

    expect(openedLogs).toEqual(['req-42']);

    // ...or pass a per-scope value by calling autoResolve yourself
    const requestScope = createAppContainer().createScope({ tags: ['request'] });
    requestScope.autoResolve({ args: ['req-43'] });

    expect(openedLogs).toEqual(['req-42', 'anonymous', 'req-43']);
  });

  it('should leave other providers lazy', function () {
    const requestScope = createAppContainer().createScope({ tags: ['request'] });

    expect(requestScope.resolve<UserRepository>('IUserRepository').findById('1')).toBe('user_1');
  });
});

Arguments

Sometimes you want to bind some arguments to provider.

• provider(appendArgs('someArgument'))
• provider(appendArgsFn(({ scope }) => [scope.resolve(Logger), 'someValue']))
• Provider.fromClass(Logger).pipe(appendArgs('someArgument'))

Dependencies as arguments

Args are passed to the constructor as-is — the library never resolves an InjectionToken (or a bare constructor) it finds in the args list. Resolve it at the call site with argsFn:

• ServiceToken.argsFn((scope) => [ValueToken.resolve(scope)]) — ValueToken is resolved from the container, its value is passed as arg
• ServiceToken.argsFn((scope) => [scope.resolve(SomeService)]) — SomeService is constructed by the container
• ServiceToken.args('literal') — literal value passed directly
• ServiceToken.args(ValueToken) — the token object itself is passed as arg

argToToken(value) is the helper for a call site that wants "resolve tokens, pass literals through": it returns an InjectionToken as-is and wraps anything else in a ConstantToken, so @inject(({ scope, args = [] }) => argToToken(args[0]).resolve(scope)) accepts either.

Positional arg injection with arg(index), args, and argsFn

Constructor parameters that should pick up positional args from ProviderOptions must be annotated with @inject(arg(index)). Parameters without @inject resolve to undefined.

• @inject(arg(0)) — resolves the first element of the args array passed at resolution time
• @inject(args) — resolves the whole runtime args array
• Works together with token.args(...) / token.argsFn(...) to pass typed dependencies through the args context

argsFn(predicate) is the general form: it iterates the runtime args array and returns the first argument matching predicate(value, index) — think args.find(predicate). arg(index) is just a shortcut for matching by position: arg(0) is argsFn((value, index) => index === 0). args is ({ args }) => args, i.e. it returns the runtime args array as-is. Every InjectFn receives one ProviderOptions object — { scope, args, lazy } — where args is the runtime args array.

findOrFail(predicate) is the strict counterpart for singleton() cache keys — singleton(findOrFail(isUserId)) keys a per-argument singleton, for example. It receives the full runtime args array, returns the first argument matching predicate(value), and throws ArgumentNotFoundError when none does, instead of silently handing out undefined.

Runtime args flow through tokens

Every container-backed token (`Single