IoC Container for Express

A very simple IoC container for Node/Express.

Principles used for this container are outline in this medium article: https://medium.com/@ismayilkhayredinov/building-a-scoped-ioc-container-for-node-express-8bf082d9887

Installation

yarn add @arckinteractive/express-ioc

Usage

You can construct a new container from an array of service definitions:

import { Container } from '@arckinteractive/express-ioc';

const definitions = [
    {
        name: 'serviceA',
        factory: () => {
            return {
                foo: process.env.FOO,
            }
        },
    },
    {
        name: 'serviceF',
        factory: (serviceA) => {
            return `I am not a ${serviceA.foo}`;
        },
        dependencies: ['serviceA'],
        options: {
            scoped: true,
        }
    }
];

const services = Container.create(definitions);

Each definition has a name, factory, dependencies and options.

A factory is function/constructor that will receive dependencies as arguments. You can register new services at runtime, after container has been created.

// Service factory as a class name
class ServiceBConstructor {
    constructor (serviceA) {
        this.serviceA = service;
    }
    
    doStuff() {
        
    }
}

// Service as a plain object
const serviceC = {};

// Scoped service (bound to a specific express request, e.g. session)
const serviceD = (serviceA) => {
    return {};
};

services.register('serviceB', ServiceBConstructor, ['serviceA']);
services.register('serviceC', () => serviceC);
services.register('serviceD', serviceD, ['serviceA', 'serviceC'], { scoped: true });

Once you access a service by its name, it's turned into a singleton, and you get the same instance of the service on consecutive calls:

const serviceA = services.get('serviceA');
// or
const { serviceB } = services;

Express will be instantiated when you create a new container and injected as a service after being bound to a cls-hooked namespace, so be sure to use the same express instance, when registering middleware.

// some middleware in some external module
export default (req, res, next) => {
    const services = req.app.get('services');
                   
    services.serviceA.doStuff();
                   
    next();
}

// your app booting module
import Container from 'express-ioc';
import middleware from './some-external-module';

const services = Container.create();

const { express } = services;

express.use(middleware);