IoC Container for Typescript

This is a lightweight annotation-based dependency injection container for typescript.

Table of Contents

• IoC Container for Typescript
  • Installation
  • Configuration
  • Basic Usage
  • @Scoped
  • @Provider
  • @Provides
  • @AutoWired
  • @The Container Class
    • Registering from multiple files
  • Circular injections
  • Custom decorators
  • A note about classes and interfaces
  • Best practices
  • Restrictions

Installation

This library only works with typescript. Ensure it is installed:

npm install typescript -g

To install @typenode/ioc:

npm install @typenode/ioc

Configuration

@typenode/ioc requires the following TypeScript compilation options in your tsconfig.json file:

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

Basic Usage

import {AutoWired, Inject} from "@typenode/ioc";

class PersonDAO {
  @Inject
  restProxy: PersonRestProxy;
}

That's it. You can just call now:

let personDAO: PersonDAO = new PersonDAO();

And the dependencies will be resolved.

You can also inject constructor parameters, like:

class PersonService {
  private personDAO: PersonDAO;
  constructor( @Inject personDAO: PersonDAO ) {
    this.personDAO = personDAO;
  }
}

and then, if you make an injection to this class, like...

class PersonController {
  @Inject
  private personService: PersonService;
}

The container will create an instance of PersonService that receives the PersonDAO from the container on its constructor. But you still can call:

let personService: PersonService = new PersonService(myPersonDAO);

And pass your own instance of PersonDAO to PersonService.

Note that any type that have a constructor can be injected.

class PersonController {
  @Inject
  private personService: PersonService;

  @Inject
  creationTime: Date;
}

Inheritance

You don't have to do anything special to work with sub-types.

abstract class BaseDAO {
  @Inject
  creationTime: Date;
}

class PersonDAO extends BaseDAO {
  @Inject
  private personRestProxy: PersonRestProxy;
}

class ProgrammerDAO extends PersonDAO {
  @Inject
  private programmerRestProxy: PersonRestProxy;
}

The above example will work as expected.

Scopes

You can use scopes to manage your instances as:

@Singleton 
class PersonService {
  @Inject
  private personDAO: PersonDAO;
}

class PersonController {
  @Inject
  private personService: PersonService;

  @Inject
  creationTime: Date;
}

So, we can create a lot of PersonController instances, but all of them will share the same singleton instance of PersonService

let controller1: PersonController = new PersonController();
let controller2: PersonController = new PersonController();

We have two pre defined scopes (Scope.Singleton and Scope.Local), but you can define your own custom Scope. You just have to extends the Scope abstract class;

class MyScope extends Scope { 
  resolve(iocProvider:Provider, source:Function) {
    console.log('created by my custom scope.')
    return iocProvider.get();
  }
}
@Scoped(new MyScope()) 
class PersonService {
  @Inject
  private personDAO: PersonDAO;
}

Providers

Providers can be used as a factory for instances created by the IoC Container.

const personProvider: Provider = { 
  get: () => { return new PersonService(); }
};
@Scoped(new MyScope()) 
@Provided(personProvider)
class PersonService {
  @Inject
  private personDAO: PersonDAO;
}

Providing implementation for base classes

It is possible to tell the container to use one class as the implementation for a super class.

class PersonDAO extends BaseDAO {
  @Inject
  private personRestProxy: PersonRestProxy;
}

@Provides (PersonDAO)
class ProgrammerDAO extends PersonDAO {
  @Inject
  private programmerRestProxy: PersonRestProxy;
}

So, everywhere you inject a PersonDAO will receive a ProgrammerDAO instance instead. However, is still possible to create PersonDAO instances through its constructor, like:

// a personDAO instance will be returned, 
// with its dependecies resolved by container
let personDAO: PersonDAO = new PersonDAO(); 

The @AutoWired annotation

The @AutoWired annotation transforms the annotated class, changing its constructor. So, any auto wired class will have its instantiation delegated to the IoC Container even when its constructor is called directly.

It is usefull, for example, to avoid that a Singleton class be instantiated directly.

@Singleton 
@AutoWired 
class PersonService {
  @Inject
  private personDAO: PersonDAO;
}

If anybody try to invoke:

new PersonService();

That instantiation will be delegated to the container. In the case of a Singleton class, the container will not allow more than one instantiation and it could cause a TypeError.

The Container class

You can also bind types directly to Container resolution.

// it will override any annotation configuration
Container.bind(PersonDAO).to(ProgrammerDAO).scope(Scope.Local); 

// that will make any injection to Date to return 
// the same instance, created when the first call is executed.
Container.bind(Date).to(Date).scope(Scope.Singleton); 

// it will ask the IoC Container to retrieve the instance.
let personDAO = Container.get(PersonDAO); 

You can use the Ioc Container with AutoWired classes and with non AutoWired classes.

class PersonDAO {
  @Inject
  private personRestProxy: PersonRestProxy;
}

Container.bind(PersonDAO); 
let personDAO: PersonDAO = Container.get(PersonDAO); 
// or
let otherPersonDAO: PersonDAO = new PersonDAO(); 
// personDAO.personRestProxy is defined. It was resolved by Container.

Singleton scopes also received a special handling.

@AutoWired
@Singleton
class PersonDAO {
}

let p: PersonDAO = new PersonDAO(); // throws a TypeError. Autowired Singleton classes can not be instantiated

const personProvider: Provider = { 
  get: () => { return new PersonDAO(); }
};
Container.bind(PersonDAO).provider(personProvider); //Works OK

Container.bind(PersonDAO).scope(Scope.Local); // Now you are able to instantiate again
let p: PersonDAO = new PersonDAO(); // Works again.

You can use snapshot and restore for testing or where you need to temporarily override a binding.

describe('Test Service with Mocks', () => {

    before(function () {
        // Hack for lazy loading (mentioned elsewhere in docs)
        MyIoCConfigurations.configure();

        // Store the IoC configuration for IService
        Container.snapshot(IService);
        
        // Change the IoC configuration to a mock service.
        Container.bind(IService).to(MockService);
    });

    after(function () {
        // Put the IoC configuration back for IService, so other tests can run.
        Container.restore(IService);
    });

    it('Should do a test', () => {
        // Do some test
    });
});

Registering from multiple files

Typescript-ioc does not scan any folder looking for classes to be registered into the Container. Your classes must be previously imported.

So, when you import a file, the decorators around the classes are activated and your decorated classes are registered into the IoC Container. However, if you have some types that are not explicitly imported by your code, you need to tell the IoC Container that they must be included.

For example, suppose:

abstract class PersonDAO {
  abstract save(person: Person);
}

@Provides (PersonDAO)
class PersonDAOImpl implements PersonDAO {
  // ...
}

If PersonDAOImpl is saved in a file that is not explicitly imported by your code, you will need to manually add it to the Container.

You can do this through Container.bind(), as previously showed, or you can use the ContainerConfig class to configure the sources to be included:

Circular injections

There is a known issue in language that it can't handle circular references. For example:

// One.ts
export class One {
    @Inject two: Two;
}

// Two.ts
export class Two {
    @Inject one: One;
}

To fix them you need to specify a type in a function this way:

// One.ts
export class One {
    @Inject(type => Two) two: Two;
}

// Two.ts
export class Two {
    @Inject(type => One) one: One;
}

Same for constructor injections.

Custom decorators

You can create your own decorators which will inject your given values for your service dependencies. For example:

// Logger.ts
export function Logger() {
    return function(target: any, propertyName: string, index?: number) {
        const logger = new ConsoleLogger();
        Container.defineHandler({ target, propertyName, index, value: () => logger });
    };
}

// LoggerInterface.ts
export interface LoggerInterface {

    log(message: string): void;

}

// ConsoleLogger.ts
import {LoggerInterface} from "./LoggerInterface";

export class ConsoleLogger implements LoggerInterface {

    log(message: string) {
        console.log(message);
    }

}

// UserRepository.ts
export class UserRepository {

    constructor(@Logger() private logger: LoggerInterface) {
    }

    save(user: User) {
        this.logger.log(`user ${user.firstName} ${user.secondName} has been saved.`);
    }

}

A note about classes and interfaces

Typescript interfaces only exists at development time, to ensure type checkings. When compiled, they generates nothing to runtime code. It ensures a good performance, but also means that is not possible to use interfaces as the type of a property being injected. There is no runtime information that could allow any reflection on interface type. Take a look at https://github.com/Microsoft/TypeScript/issues/3628 for more information about this.

So, this is not supported:

interface PersonDAO {
  get(id: string): Person;
}

@Provides (PersonDAO) // NOT SUPPORTED
class ProgrammerDAO implements PersonDAO {
  @Inject
  private programmerRestProxy: PersonRestProxy;

  get(id: string): Person
  {
      // get the person and return it...
  }
}

class PersonService {
  @Inject // NOT SUPPORTED
  private personDAO: PersonDAO;
}

However there is no reason for panic. Typescript classes are much more than classes. It could have the same behavior that interfaces on other languages.

So it is possible to define an abstract class and then implement it as we do with interfaces:

abstract class PersonDAO {
  abstract get(id: string): Person;
}

@Provides (PersonDAO) // It works
class ProgrammerDAO implements PersonDAO {
  @Inject
  private programmerRestProxy: PersonRestProxy;

  get(id: string): Person
  {
      // get the person and return it...
  }
}

class PersonService {
  @Inject // It works
  private personDAO: PersonDAO;
}

Best practices

It is prefereable to configure your Singleton classes using @AutoWired. It is safer because ensure that all configurations will be applied even if its constructor is called directly by the code.

Configure default implementations for classes using @Provides annotation. If you need to change the implementation for some class, you just configure it direct into IoC Container.

abstract class PersonDAO {
  abstract get(id: string): Person;
}

@Provides (PersonDAO) 
class ProgrammerDAO implements PersonDAO {
}

// And later, if you need...
class ManagerDAO implements PersonDAO {
}

Container.bind(PersonDAO).to(ManagerDAO); //It will override any annotation

Another good practice is to group all your container configurations. It is easier to manage.

export default class MyIoCConfigurations {
  static configure(){ 
    Container.bind(PersonDAO).to(ManagerDAO); 
    Container.bind(DatabaseProvider).to(MyDatabaseProvider).scope(Scope.Singleton); 
    Container.bind(RestEndPointResolver).provider(MyRestEndPoints).scope(Scope.Singleton); 
    // ...
  }
}

// and call..
MyIoCConfigurations.configure();