injection-js

What is injection-js?

injection-js is a lightweight dependency injection library for JavaScript and TypeScript, inspired by Angular's dependency injection system. It allows developers to manage dependencies in a clean and modular way, promoting better code organization and testability.

What are injection-js's main functionalities?

Basic Dependency Injection

This example demonstrates basic dependency injection using injection-js. The `Car` class depends on the `Engine` class, and the injector resolves and provides the dependencies automatically.

const { ReflectiveInjector } = require('injection-js');

class Engine {
  start() {
    console.log('Engine started');
  }
}

class Car {
  constructor(engine) {
    this.engine = engine;
  }
  drive() {
    this.engine.start();
    console.log('Car is driving');
  }
}

const injector = ReflectiveInjector.resolveAndCreate([Engine, Car]);
const car = injector.get(Car);
car.drive();

Injection Tokens

This example shows how to use injection tokens to inject primitive values or non-class dependencies. The `ApiService` class depends on an API URL, which is provided using an injection token.

const { ReflectiveInjector, InjectionToken } = require('injection-js');

const API_URL = new InjectionToken('apiUrl');

class ApiService {
  constructor(apiUrl) {
    this.apiUrl = apiUrl;
  }
  getData() {
    console.log(`Fetching data from ${this.apiUrl}`);
  }
}

const injector = ReflectiveInjector.resolveAndCreate([
  { provide: API_URL, useValue: 'https://api.example.com' },
  { provide: ApiService, useClass: ApiService, deps: [API_URL] }
]);

const apiService = injector.get(ApiService);
apiService.getData();

Hierarchical Injectors

This example demonstrates hierarchical injectors, where a child injector can inherit dependencies from a parent injector. The `Car` class is resolved in the child injector, while the `Engine` class is resolved in the parent injector.

const { ReflectiveInjector } = require('injection-js');

class Engine {
  start() {
    console.log('Engine started');
  }
}

class Car {
  constructor(engine) {
    this.engine = engine;
  }
  drive() {
    this.engine.start();
    console.log('Car is driving');
  }
}

const parentInjector = ReflectiveInjector.resolveAndCreate([Engine]);
const childInjector = parentInjector.resolveAndCreateChild([Car]);

const car = childInjector.get(Car);
car.drive();

Other packages similar to injection-js

inversify

Inversify is a powerful and flexible inversion of control (IoC) container for JavaScript and TypeScript. It provides a rich set of features for dependency injection, including support for decorators, middleware, and more. Compared to injection-js, Inversify offers a more feature-rich and extensible API, but it may be more complex to set up and use.

tsyringe

tsyringe is a lightweight dependency injection container for TypeScript and JavaScript. It uses decorators and reflection to manage dependencies, making it easy to use and integrate into existing projects. Compared to injection-js, tsyringe is more focused on TypeScript and provides a simpler API for common use cases.

awilix

Awilix is a powerful dependency injection container for JavaScript and TypeScript, designed to be easy to use and flexible. It supports various registration methods, including class, function, and value registrations. Compared to injection-js, Awilix offers a more modern and flexible API, with a focus on ease of use and developer experience.

README

Dependency Injection

Dependency injection library for JavaScript and TypeScript in 5.2K. It is an extraction of the Angular's dependency injection which means that it's feature complete, fast, reliable and well tested.

Up-to-date with Angular 4.1.

How to use?

$ npm i injection-js --save

Note that for ES5 Class syntax and TypeScript you need a polyfill for the Reflect API. You can use, for instance, reflect-metadata, or core-js (core-js/es7/reflect).

TypeScript

import 'reflect-metadata';
import { ReflectiveInjector, Injectable, Injector } from 'injection-js';

class Http {}

@Injectable()
class Service {
  constructor(private http: Http) {}
}

@Injectable()
class Service2 {
  constructor(private injector: Injector) {}
  
  getService(): void {
    console.log(this.injector.get(Service) instanceof Service);
  }
  
  createChildInjector(): void {
    const childInjector = ReflectiveInjector.resolveAndCreate([
      Service
    ], this.injector);
  }
}

const injector = ReflectiveInjector.resolveAndCreate([
  Service,
  Http
]);

console.log(injector.get(Service) instanceof Service);

Note: you will need to enable the TypeScript flags experimentalDecorators and emitDecoratorMetadata to make this work.

ES6

const { Inject, ReflectiveInjector } = require('injection-js');

class Http {}

class Service {
  static get parameters() {
    return [new Inject(Http)];
  }

  constructor(http) {
    this.http = http;
  }
}

const injector = ReflectiveInjector.resolveAndCreate([Http, Service]);

console.log(injector.get(Service) instanceof Service);

ES5

require('reflect-metadata');
var di = require('injection-js');

var Http = di.Class({
  constructor: function () {}
});

var Service = di.Class({
  constructor: [Http, function (http) {
    this.http = http;
  }]
});

var injector = di.ReflectiveInjector.resolveAndCreate([Http, Service]);

console.log(injector.get(Service) instanceof Service);

For full documentation click here, here and here.

License

MIT