Injector

A lightweight, type-aware dependency injection container for JavaScript/TypeScript (with JSDoc support), supporting class and function dependencies with type inference.

Features

• Type Inference: Automatically infers dependency types
• Class & Function Support: Register instances from classes or factory functions
• Error Handling: Throws clear errors for unregistered dependencies
• Zero Dependencies: Tiny footprint (< 1KB minified)

Installation

npm install "@collidor/injector"

Usage

Basic Class Example

import { Injector } from '"@collidor/injector"';

// Create injector
const injector = new Injector();

// Register a class instance
class DatabaseService {
  connect() { return 'Connected!'; }
}

injector.register(DatabaseService, new DatabaseService());

// Inject the instance (type inferred as DatabaseService)
const db = injector.inject(DatabaseService);
console.log(db.connect()); // "Connected!"

Function Dependency Example

// Register a factory function
const configFactory = () => ({ env: 'production' });
injector.register(configFactory, configFactory());

// Inject the function result (type inferred as { env: string })
const config = injector.inject(configFactory);
console.log(config.env); // "production"

Register in class properties:

import {Database} from './database.ts'

class Service {
    private database = inject(Database)

    getData() {
        return this.database.query();
    }
}

Interdenpendency or race condition

If two classes depend on each other in any place except the constructor, we can use getters or get the instances directly in the Methods:

import {Database} from './database.ts'

class Service {
    get database(): Database {
        return inject(Database);
    }

    getData() {
        return this.database.query();
    }
}

Error Handling

try {
  injector.inject(UnregisteredService); // Throws error
} catch (err) {
  console.error(err.message); // "No instance registered for type: UnregisteredService"
}

API

Injector

register(type, instance)

• Parameters:
  • type: Constructor | Function | Symbol | Object (dependency identifier)
  • instance: Value to store
• Returns: void

Registers a dependency instance.

inject(type)

• Parameters:
  • type: Constructor | Function | Symbol | Object (dependency identifier)
• Returns:

  T extends Type<infer M> ? M : T extends (...args: any[]) => infer R ? R : any
  

• Throws: Error if no instance is registered for type

Retrieves a dependency instance.

Type Inference

Works with both class constructors and factory functions:

// Class registration
class AuthService {
  login() { /* ... */ }
}
injector.register(AuthService, new AuthService());
const auth = injector.inject(AuthService); // Inferred as AuthService

// Function registration
const loggerFactory = () => ({ log: (msg: string) => console.log(msg) });
injector.register(loggerFactory, loggerFactory());
const logger = injector.inject(loggerFactory); // Inferred as { log: (msg: string) => void }

Contributing

1. Fork the repository
2. Create a feature branch
3. Submit a pull request

License

MIT