Beaver - Dependency Injection Container for NodeJS

Lean dependency injection container for NodeJS based on parameter naming, which helps instantiating and referencing dependencies.

Installation

You can get the latest release using:

$ npm install beaver-di

or:

$ yarn add beaver-di

Terminology

There are two type of values we are going to hold in our Dependency Injection Container

Name	Description
factories	Functions used to instantiate a dependency, typically you will use a factory when instantianting a dependency that depends on other dependencies
dependencies	Values that are fixed dependencies, typically environment variables or constant values

Usage

Define a beaver.config.js file where we instantiate the Dependency Injection Container. This will be the only place where coupling occurs

Here you can define either a factory (used to instantiate a dependency) or a plain dependency that doesn't require any other dependency.

// ./beaver.config.js
import userController from './userController';
import userService from './userService';
import database from './database';
import beaver from 'beaver-di';

export default beaver(
  // Factories
  {
    userController,
    userService,
    database,
  }, 
  // Dependencies
  {
    helloString: 'helloWorld',
    db: {
      connectionString: 'postgres://',
    },
  },
);

Now just require this file at the top level of you application.

Remember that as this is a property naming based dependency injection, meaning that you will need to match your dependency by name on the object passed to beaver. If you need more control over the naming of parameters passed to a factory, you can make use of the connect(factory, dependencies) API

// ./userController.js

// we defined on beaver.config.js userService module on the property userService
export default (userService, helloString) => {
  // this module does not depend on '/userService.js' but it uses it by the dependecy injected argument
  
  const createUser = async (name) => {
    await userService.create({name})
    ...
  };
  
  const salute = () => helloString;
  
  return {
    createUser,
    salute,
  };
};

Examples

You can find a simple example of how to build an Express app using Beaver DI in the examples directory

Walkthrough

We first define the beaver.config.js file

import todo from './api/todo';
import todoController from './api/todo/todo.controller';
import todoService from './api/todo/todo.service';

export default beaver(
  {
    todo,
    todoController,
    todoService,
  },
  {
    database: {
      ...
    },
  },
);

To continue, in our routes module, we get from beaver the instance of todo factory

import beaver from './beaver.config';

export default (app) => {
  const todo = beaver.get('todo');
  app.use('/api/todo', todo);
};

As todo factory dependes on todoController and todoController depends on todoService, all instances are created when executing const todo = beaver.get('todo');

todo module

import { Router } from 'express';

export default (todoController) => {
  const router = Router();

  router.get('/', todoController.getAll);
  router.post('/', todoController.create);
  router.get('/:id', todoController.get);
  router.delete('/:id', todoController.delete);

  return router;
};

todoController module

export default (todoService) => {
  ...
  return {
    getAll,
    get,
    create,
    delete: deleteTodo,
  };
};

todoService module

export default (database) => {
  ...
  return {
    getAll,
    getById,
    create,
    delete: deleteTodo,
  };
};

API

Creating an instance

Core functionality. Used to instantiate Beaver Dependency Injection Container

import beaver from 'beaver-di';

beaver(factories, dependencies)

Connect API

Used to provide flexibility when injecting properties into a factory.

Notes

• Values in connect method need to be a string to access dependency injected in a object-like structure.
• When trying to access a dependency which is in a object-like structure, you will always need the connect API (in this example, the connectString parameter.

import { connect } from 'beaver-di';


const factory = (connectionString, service, controller) => {
  ...
};

export default connect(factory, { service: 'userService', controller: 'userController', connectionString: 'databases.postgres.connectionString' });

Instance methods

beaver.get(name)

Retrieve instance of dependency

beaver.factory(name, factory)

Assign dynamically to a specific name a factory function that when executed will create an instance of dependency

beaver.register(name, dependency)

Assign dynamically to a specific name, an instance of a dependency. This can also be used to register constants i.e. beaver.register('TOKEN', 'secretToken!').