Dependency Injection example for NodeJS - Source: https://auth0.com/blog/developing-well-organized-apis-with-nodejs-joi-and-mongo/

container.example.js

// This file is to register independent modules and dependencies of each entities, usecase, etc.
//
// All this is fiction:
//  infrastructure -> External frameworks
//  interfaces -> Layer of abstraction of frameworks
//

import serviceLocator from './config/serviceLocator'                                                                                                 

serviceLocator.register('webserver', () => { // Generic name
    return require('./configs/express.js'); // This is independent
})

serviceLocator.register('database', () => {
    return require('./configs/mongoose.js');  // Other independent
})

serviceLocator.register('userService', (serviceLocator) => {
    const userService = require('./UserService')({ // This create a object. The class need database connections
        database: serviceLocator.get('database')
    })

    return userService;
})

module.exports = serviceLocator

index.example.js

import serviceLocator from './container'

const database = serviceLocator.get('database')
const webserver = serviceLocator.get('webserver')

function main () {
    database.connect();
    webserver.start();
}

main();

serviceLocator.js

class ServiceLocator {
    constructor () {
        this.dependencyMap = {};
        this.dependencyCache = {};
    }

    register (name, constructor) {
        validate(name, constructor)
                                                                                                                                                     
        this.dependencyMap[name] = constructor;
    }

    get (name) {
        const constructor = this.dependencyMap[name];

        validate(name, constructor);

        if (this.dependencyCache[name] === undefined) {
            const dependency = constructor(this);

            if (dependency)
                this.dependencyCache[name] = dependency;
        }

        return this.dependencyCache[name];
    }

    clear () {
        this.dependencyCache = {};
        this.dependencyMap = {};
    }
}

function validate (name, constructor) {
    validateName(name);
    validateConstructor(name, constructor);
}

function validateName (name) {
    if (typeof name !== 'string' && !name)
        throw new Error('Invalid dependency name provided');
}

function validateConstructor (name, constructor) {
    const isNotFunctionError = ': Dependency constructor is not a function';

    if (typeof constructor === 'function')
        throw new Error(name + isNotFunctionError);
}

module.exports = new ServiceLocator();