zombiebox-extenstion-dependency-injection

ZombieBox extension that adds Dependency Injection support.

It operates by scanning application source code, finding injection targets and services that provide classes and, building dependency graph and generating a BaseServiceContainer class that handles their initialization, cross-dependencies and populates targets properties with injection values.

Configuration

module.exports = () => ({
	extensions: {
		di: {
			services: { /* Dictionary of explicitly configured services */ },
			servicesAutodetect: [ /* Array of service detection roots */]
		}
	}	
})

Services

Services are classes that are meant to be injected. They are listed in config either explicitly, or as part of automatic detection roots.

Explicit declaration

Explicit services are configured under extensions.di.services filed as an object with its keys being services names and values – objects configuring the way service should be instantiated and its dependencies.

Configuration fields are:

• _class – service class name
• _import – ImportType ("default" or "partial"), the way ES6 modules should be imported
• _path – path to file with this class declaration
• _group - semantic group this service will be put into

The rest of the keys are dependencies of this service.

Example:

movie: {
	_class: 'Movie',
	_group: 'controller',
	_import: ImportType.DEFAULT,
    _path: '/controllers/movie/movie.js',
	sceneMovieCard: '{MovieCard}',
	sceneMovieList: '{MovieList}',
	repositoryMovie: '@repositoryMovie'
}

This declares that:

• MovieController class should imported from /controllers/movie/movie.js and constructed in service container
• It can be imported as default import
• Its instance should be named movie
• And placed into controller namespace
• It depends on repositoryMovie service
• It depends on MovieCard and MovieList classes

And will generate BaseServiceContainer class with the following structure (simplified):

// .generated/dependency-injection/base-service-container.js
import Movie from '<APP_ALIAS>/controllers/movie/movie.js';

export default class{
	constructor() {
		this.movie = new MovieController();
	}
}

Automatic detection

Services can be automatically detected under service roots declared in servicesAutodetect config key. The default value for this field contains scenes and service folders.

Root entry can either be a string, or object with fields group and directory

{
   group: 'string',
   directory: 'string'
}

Dependency detection

Properties

Public class properties with type annotation comment starting with :inject:

class MovieController {
	constructor() {
		/**
		 * @type {MovieList}:inject
		 */
		this.sceneMovieList;
	}
}

or:

/**
 * @type {MovieList}:inject
 */
MovieController.prototype.sceneMovieList;

Setter methods

Methods with parameters that have their description start with :inject

class MovieController {
	/**
	 * @param {MovieList} sceneMovieList :inject
	 */
	setSceneMovieList(sceneMovieList) {
		this._sceneMovieList = sceneMovieList;
	}
}

Constructor

Constructor parameters that have their description start with :inject

class MovieController {
	/**
	 * @param {MovieList} sceneMovieList :inject
	 * @param {MovieCard} sceneMovieCard :inject
	 */
	constructor(sceneMovieList, sceneMovieCard) {
		this._sceneMovieList = sceneMovieList;
		this._sceneMovieCard = sceneMovieCard;
	}
}

Dependency matching

Dependency injection will match classes as following:

• Class exactly matching declared dependency
• Class inheriting from declared dependency
• Class implementing interface declared in dependency

If there are several classes matching declared dependency there's no guarantee which one will be injected.