mikro-di

Simple ES6 DI container for node.js, that honours convention over configuration.

It works by discovering given directories and generating a simple DI container instance, which is properly type-hinted and allows auto-completion in editors like WebStorm or VS Code.

It also allows to create service definition with scalar constructor parameters (e.g. HttpClient('https://api.example.io')) and has built-in circular dependencies detection.

Inspired by https://github.com/nette/di

Installation

$ yarn add mikro-di

or

$ npm install mikro-di

Usage

DI container should be the first thing you enable in your application, so the right place for it is in the app.js file.

app.js

require('mikro-di').init(['api/services', 'api/repositories']);

And then you can require it and use it:

const di = require('mikro-di').di;
  
const ret = di.YourFunkyService.process();
console.log(ret);

Registering dependencies

You can declare you service dependencies like this:

class YourFunkyService {
  
  /**
   * @param {YourFunkyDependency1} dep1 
   * @param {YourFunkyDependency2} dep2 
   */
  constructor(dep1, dep2) {
    this.dep1 = dep1;
    this.dep2 = dep2;
  }
  
}
 
// and export it
module.exports = YourFunkyService;

Or if you like to you simple objects, you can do this:

const YourFunkyService = {
  
  $inject: ['YourFunkyDependency1', 'YourFunkyDependency2'],
  
  /**
   * @param {YourFunkyDependency1} dep1 
   * @param {YourFunkyDependency2} dep2 
   */
  constructor(dep1, dep2) {
    this.dep1 = dep1;
    this.dep2 = dep2;
  }
  
};
 
// and export it
module.exports = YourFunkyService;

When you register you service as ES6 class, you do not need the $inject property, but the jsdoc with proper type-hinting is required.

If you use plain object export, you can omit the type-hinting of constructor.

Usage in sails.js controllers

const di = require('mikro-di').di;
  
module.exports = {
 
  /** @var {YourFunkyService} funkyService */
  funkyService: di.YourFunkyService,
 
  yourHandler: function (req, res) {
    const data = this.funkyService.process(req);
    res.json(data);
  }
 
};

The @var annotation is optional.

Scalar constructor parameters

When you need to pass a scalar constructor parameter to your service, you can do so be providing a service definition via options:

class YourFunkyDependency2 {
 
  /**
   * @param {String} namespace 
   */
  constructor(namespace) {
    this.namespace = namespace;
  }
 
}
 
module.exports = YourFunkyDependency2;

const di = require('mikro-di').init(['api/services', 'api/repositories'], {
  services: {
    scalarService: `YourFunkyDependency2('funky-namespace')`,
  },
});
 
console.log(di.scalarService); // YourFunkyDependency2
console.log(di.scalarService.namespace); // 'funky-namespace'

Configuration

You can pass your configuration as a second parameter to mikro-di:

require('mikro-di').init(['api/services', 'api/repositories'], {
  logger: console.log, // defaults to null
  baseDir: '/path/to/your/app', // defaults to `process.cwd()`
  contextDir: '/path/to/your/context', // defaults to `baseDir`
  contextName: 'di.js', // defaults to `.context.js`
});

How does it work

mikro-di will discover all paths that you provide as its first parameter and generate DI context, that you can require and use in your application. It works by loading the contents of source files via fs, so the file itself is never loaded (required) before you try to access it from the di context.

The context file is generated in your baseDir and is named as .context.js. This file should be ignored via .gitignore, as it is generated code. You can adjust the path where it is stored via contextDir option and the name via contextName option.

The context file will look like this:

module.exports = {
 
  _map: {},
  
  /**
   * @returns {YourFunkyService} 
   */
  get YourFunkyService() {
    if (!this._map.YourFunkyService) {
      const YourFunkyService = require('./api/services/AsyncService.js');
      this._map.YourFunkyService = new YourFunkyService(this.YourFunkyDependency1, this.YourFunkyDependency2);
    }
    return this._map.YourFunkyService;
  },
 
  /**
   * @returns {YourFunkyDependency1} 
   */
  get YourFunkyDependency1() {
    if (!this._map.YourFunkyDependency1) {
      this._map.YourFunkyDependency1 = require('./api/services/YourFunkyDependency1.js');
    }
    return this._map.YourFunkyDependency1;
  },
 
  /**
   * @returns {YourFunkyDependency2} 
   */
  get YourFunkyDependency2() {
    if (!this._map.YourFunkyDependency2) {
      this._map.YourFunkyDependency2 = require('./api/services/YourFunkyDependency2.js');
    }
    return this._map.YourFunkyDependency2;
  },
 
};

It basically creates object with ES6 getters that will require you services and its dependencies. This way everything is loaded via lazy loading technique.

Circular dependencies detection

Before building the container, simple DFS algorithm is used to look up cyclic dependencies and when found, it raises an error.