InversifyJS

InversifyJS relies on reflect-metadata to enable decorator-based dependency injection. You must import reflect-metadata at the very top of your application's entry point before any other InversifyJS imports or decorated classes are defined.

import 'reflect-metadata';
import { Container, injectable } from 'inversify';
// ... rest of your application

The inversify package exports the primary tools for managing Dependency Injection (DI). The API is organized into three main functional areas:

1. Container Management: Using Container to manage bindings and ContainerModule to group related bindings.
2. Binding & Lifecycle: Using fluent syntax (e.g., Bind, To, In) to define how services are instantiated and their scope (BindingScope).
3. Decorators: Using @injectable to mark classes for DI, and @inject, @tagged, @optional, and others to define how dependencies are resolved.

The @inject decorator is used on constructor parameters to tell InversifyJS which identifier (a class, a string, or a symbol) should be used to resolve that specific dependency.

import { injectable, inject, Container } from 'inversify';

const TYPES = { MyService: Symbol.for('MyService') };

@injectable()
class Consumer {
  constructor(@inject(TYPES.MyService) myService: MyService) {}
}

The @injectable decorator marks a class as being eligible for injection by the InversifyJS container. This allows the container to manage the class's lifecycle and resolve its dependencies.

import { injectable, Container } from 'inversify';

@injectable()
class MyService {}

const container = new Container();
container.bind(MyService).toSelf();

When multiple implementations of the same service are bound to the container, you can use @tagged to distinguish them. Use @multiInject on the constructor parameter to request all implementations associated with a specific tag.

import { injectable, tagged, multiInject, Container } from 'inversify';

const TAG = Symbol.for('Tag');

@injectable()
@tagged(TAG)
class TaggedService {}

@injectable()
class Consumer {
  constructor(@multiInject(TAG) services: TaggedService[]) {}
}