ServiceIdentifier

Overview

ServiceIdentifier is a fundamental type that identifies services within the InversifyJS dependency injection container. It serves as a key for registering, locating, and retrieving services, acting as a bridge between service registration and resolution.

Definition

ServiceIdentifier is a union type that can be one of:

type ServiceIdentifier<TInstance = unknown> =
  | string
  | symbol
  | Newable<TInstance>
  | Function;

Where Newable is defined as:

type Newable<
  TInstance = unknown,
  TArgs extends unknown[] = any[],
> = new (...args: TArgs) => TInstance;

Usage

ServiceIdentifier is used throughout the InversifyJS API for:

1. Service Registration: Binding services to the container
2. Service Resolution: Retrieving services from the container
3. Service Configuration: Setting activation/deactivation handlers

Registration Examples

// Using a class as a service identifier (most common)
container.bind(UserService).toSelf();

// Using a string as a service identifier
container.bind("IUserService").to(UserService);

// Using a symbol as a service identifier
const userServiceId: interfaces.ServiceIdentifier<UserService> =
  Symbol("UserService");

container.bind(userServiceId).to(UserService);

// Resolving with a class identifier
const firstUserService = container.get(UserService);

// Resolving with a string identifier
const secondUserService = container.get("IUserService");

// Resolving with a symbol identifier
const thirdUserService = container.get(userServiceId);

Type Inference support

When using generics with ServiceIdentifier<T>, TypeScript can infer the resolved type. In the example above, thirdUserService is automatically typed as UserService because userServiceId was defined as ServiceIdentifier<UserService>.