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.

Why not Angular version 5 and above?

Angular version 5 deprecated the ReflectiveInjector API and introduced StaticInjector. In short, the dependency injection in the newest versions of Angular will happen entirely compile-time so reflection will not be necessary.

However, if you want to use dependency injection in your Node.js, Vue, React, Vanilla JS, TypeScript, etc. application you won't be able to take advantage of StaticInjector the way that Angular will because your application won't be compatible with Angular compiler.

This means that if you need dependency injection outside of Angular @angular/core is not an option. In such case, use injection-js for fast, small, reliable, high-quality, well designed and well tested solution.

How to use?

$ npm i injection-js
# OR
$ yarn add injection-js

Note:

For ES5 Class syntax and TypeScript you need a polyfill for the Reflect API. You can use:

• reflection (only 3kb 🔥)
• reflect-metadata
• core-js (core-js/es7/reflect)

Also for TypeScript you will need to enable experimentalDecorators and emitDecoratorMetadata flags within your tsconfig.json

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);

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);

API

For full documentation check Angular DI docs:

• Dependency Injection
• Dependency Injection in action
• Dependency Injection without Typescript

Ecosystem

This is a list of libraries that are using injection-js. If you have a suggestion on what to add, please don't hesitate to submit a PR.

Libraries

• ng-packagr Transpile your libraries to Angular Package Format. Part of the official Angular CLI.
• @martin_hotell/axios-http Injectable axios HttpClient wrapper for browser and node
• @martin_hotell/rea-di Dependency injection for React done right. Hierarchical injection on both component and service layer powered by injection-js (Angular DI framework) 🖖
• rxstack RxStack is a realtime object-oriented framework which helps you build a micro service web applications on top of other frameworks like express and socketio by adding an abstraction layer.
• ServeRX-ts Experimental Node.js HTTP framework using RxJS, built with TypeScript and optimized for serverless deployments. Features declarative routes and dependency injection powered by injection-js.

License

MIT