Visual Studio Code's "instantiation" system

decoration-ioc is a very simple inversion of control and dependency injection framework. Taken directly from Visual Studio Code, decoration-ioc provides robust service location and constructor injection with automatic dependency resolution.

Quickstart

First, make sure that the experimentalDecorators TypeScript compiler option is set to true.

Define a service interface

// Define the service.
export interface IMyService {
    _serviceBrand: undefined;

    sayHello(): string;
}

// Create a decorator used to reference the interface type.
export const IMyService = createDecorator<IMyService>('myService');

Note that the decorator has the same name as the interface. You'll only need to import IMyService!

Create a concrete implementation

export class MyService implements IMyService {
    _serviceBrand: undefined;

    sayHello() {
        return 'Hello!';
    }
}

Register the concrete type for the service

// Create a service collection where concrete implementation types are registered.
const serviceCollection = new ServiceCollection();

// Declare that the MyService class is the type that is instantiated when an IMyService is needed.
serviceCollection.set(IMyService, new Descriptor(MyService));

Creating instances

// Create an instantiation service that performs constructor injection.
// It uses the service collection to resolve dependencies and create instances.
const instantiationService = new InstantiationService(serviceCollection);

// This is a class that requires an instance of IMyService when created.
export class MyDependentClass {
    private _myService: IMyService;

    // The myService parameter is annotated with the IMyService decorator.
    constructor(@IMyService myService: IMyService) {
        this._myService = myService;
    }

    makeMyServiceSayHello() {
        console.log(this._myService.sayHello());
    }
}

// Create an instance of myDependentClass.
const myDependentClass = instantiationService.createInstance(MyDependentClass);
myDependentClass.makeMyServiceSayHello();