Zero dependency IOC container for Node

Installation

npm install ioc-node

Instantiate

// index.js

global.ioc = require('ioc-node')(__dirname)

Usage

Imagine the following class

class UserService {
    constructor(database) {
        this.database = database
    }
}

You can inject dependencies using

ioc.bind('userService', () => new UserService(new Database))

and later make use of the binding with

ioc.use('userService').create({ id: 1})

If you don't want to create a new instance every time you use ioc.use, create the binding with ioc.singleton instead of ioc.bind.

ioc.singleton('userService', () => new UserService(new Database))

ioc.use('userService').create({ id: 1})
ioc.use('userService').create({ id: 2}) // uses same instance

Faking

You can easily fake bindings in your tests!

class TestableDatabase {
    insert() { return true }
}

ioc.fake('userService', () => new UserService(new TestableDatabase))

const userService = ioc.use('userService')
// assert...

ioc.restore('userService') // remove the fake again

Global Require

The use method can also require files globally from any point in the app.

const User = ioc.use('app/models/User')

Automatic Injection

It might be cumbersome to always add bindings, that's why ioc-node also supports automatic injection. Since there are no static types we have to workaround a little to get this working.

Instead of registering bindings in the service provider using ioc.bind('userService', () => new UserService(new Database)), you can link to the dependency directly in the class

// App/Services/UserService
class UserService {
    static get inject() {
        return ['path/to/Database']
    }

    constructor(database) {
        this.database = database
    }
}

And instead of newing up the class manually, we do

const userService = ioc.make('App/Services/UserService') // will use ioc.use to resolve dependency

or

const UserService = ioc.use('App/Services/UserService')
const userService = ioc.make(UserService)

You can also pass additional arguments to the constructor

const userService = ioc.make('App/Services/UserService', 1, 2, 3, 4)

Faking Automatic Injection

In the above case, you can still use ioc.fake to provide a fake database or a fake userService since ioc.make('App/Services/UserService') uses ioc.use under the hood. In addition, every auto injected dependencies (e.g. "path/to/Database") also gets resolved using ioc.use.

Alternatively you can just new up an instance of the class manually.

const UserService = ioc.use('App/Services/UserService')
class TestableDatabase {
    insert() { return true }
}

const userService = new UserService(new TestableDatabase))

Aliases

When using ioc.bind or ioc.singleton we can access the bindings using the key we provide. Global requires and automatic injections don't provide that flexibility out of the box. Say the file Cache.js is inside App/Utils/. You have to require it using ioc.use('App/Utils/Cache'), while you might actually want to do ioc.use('Cache').

For this you can use aliases.

// in service provider
ioc.alias('Cache', 'App/Utils/Cache')

// anywhere
const cache = ioc.make('Cache')
//or
const Cache = ioc.use('Cache')

We can also use the alias for automatic injections.

class UserService {
    static get inject() {
        return ['Cache']
    }

    // ...
}

How ioc.use resolves dependencies

1. Look in fakes (ioc.fake)
2. Look in container (ioc.bind / ioc.singleton)
3. Look in aliases (ioc.alias)
   1. Repeat process with resolved name
4. Native require from root of the project

Creating Providers

If you extract code into separate npm modules, you can create a provider that can be easily consumed by the ioc container.

Say you have the following module

class StringTransformer {
    toUpperCase(value) {
        return value.toUpperCase()
    }
}

module.exports = StringTransformer

In the same module, you can create a provider like this

class StringTransformerProvider {
    register(ioc, namespace) {
        ioc.singleton(namespace, () => new StringTransformer)
    }
}

module.exports = StringTransformerProvider

and inside the service provider of your app, you can consume this provider

ioc.consume('App/StringTransformer', StringTransformerProvider)