Nodejs-ioc

About

Nodejs-ioc is an inversion of control (IoC) container for JavaScript apps.

An IoC container uses a class constructor to identify and inject its dependencies.

Nodejs-ioc allows JavaScript developers to write code that adheres to the SOLID principles.

Installation

You can get the latest release using npm:

$ npm install nodejs-ioc --save

:warning: Important! Nodejs-ioc requires JavaScript ES6 

The Basics

Let’s take a look at the basic usage and APIs of Nodejs-ioc with JavaScript:

Step 1: Declare your types

const {Type} = require("nodejs-ioc");

const TYPES = {
    AUTH_SERVICE : Type.for('AUTH_SERVICE'),
    USER_SERVICE : Type.for('USER_SERVICE'),
    CONFIG : Type.for('CONFIG'),
    TEST_SERVICE : Type.for('TEST_SERVICE'),
};

Note: It is recommended to use Types but Nodejs-ioc also support the usage of string literals.

Step 2: Create and configure a Container

const {Container, inject} = require("nodejs-ioc");

class UserService {
}

class AuthService {
    constructor(){
        this.config = inject(TYPES.CONFIG);
        console.log('AuthService generated');
    }
}

const config = {
    conf:'conf'
};

const container = new Container();
container.bind(TYPES.USER_SERVICE).to(UserService);

module.exports = { container }

bind options

Binds to a singleton class

container.bind(TYPES.AUTH_SERVICE).toSingleton(AuthService);

Binds to a constant value

container.bind(TYPES.CONFIG).toConstantValue(config);

Step 3: Resolve dependencies

You can use the method get from the container class to resolve a dependency.

const authService = container.get(TYPES.AUTH_SERVICE);

expect(authService.config.conf).eql("conf"); // true

As we can see the config was successfully resolved and injected into AuthService.

inject

There are two important things to remember when using inject:

• It must be used inside a constructor
• The requested dependencies will be injected after the class instance is created — i.e., not inside the constructor (the inject keyword only marks the class members as flags and doesn't injects the dependency immediately).

For catching the dependencies' injection we can use onDependenciesInjected method

class AuthService {
    constructor(){
        this.config = inject(TYPES.CONFIG);
        //config is not injected yet
        console.log('AuthService generated');
    }

    onDependenciesInjected(){
        console.log('AuthService dependencies were injected', this.config);
    }

}

Injecting a Provider (asynchronous Factory)

Binds an abstraction to a Provider. A provider is an asynchronous factory, this is useful when dealing with asynchronous I/O operations.

container.bind(TYPES.TEST_SERVICE).toProvider((context) => {
    return (args) => {
        console.log(args);
        return new Promise((resolve) => {
            let userService = context.container.get(TYPES.USER_SERVICE);
            resolve(userService);
        });
    }

});

const testServiceProvider = container.get(TYPES.TEST_SERVICE);
testServiceProvider("hello").then((userService)=>{
    console.log(userService);
});

Lazy inject

Using lazyInject allows the container to inject dependencies into objects that are not bound to it. For example, when using a service in an Express middleware that exists inside a container.

lazyInject works differently from the inject method provided above, since it injects the dependency immediately (uses the get method)

lazyInject is linked to a specific container, hence needs to be exported after instantiating the container.

const lazyInject = container.lazyInject;

class HttpRequest{

    constructor(){
        this.authService = lazyInject(TYPES.AUTH_SERVICE);
        //authService is now injected
        console.log('HttpRequest generated', this.authService)
    }
}

const httpRequest = new HttpRequest();