@decouplejs/core

A dependency injection library based on IoC Container. Dependency Injection implementation for Node.js projects written with Typescript. Build a container and permit it for all dependencies. Get all injectable objects easily without use new keyword. It's light-weight library and easy-to-use.

Installation

npm i @decouplejs/core

And add below to compilerOptions in tsconfig.json

"experimentalDecorators": true

Usage

Lets think about you have two classes which are UserController and UserService.

UserController have a dependency to UserService which is declared with @inject decorator.

export class UserController {
  constructor(
    @inject(USER_SERVICE)
    private userService: UserService
  ) {}

  print() {
    console.log("UserController");
    this.userService.print();
  }
}

export class UserService {
  constructor() {}

  print() {
    console.log("UserService");
  }
}

When we used @inject decorator, USER_SERVICE binding key was declared. Lets define this binding keys.

Create a keys.ts file and define binding keys to be associated with above classes like below:

export const USER_CONTROLLER = BindingKey.create("user.controller");
export const USER_SERVICE = BindingKey.create("user.service");

Now, create a Container and introduce your classes to IoC Container via its .injectable() function with binding keys that are defined before.

const container = new Container();
container.injectable(USER_CONTROLLER, UserController);
container.injectable(USER_SERVICE, UserService);

Finally, if you want to create and use a UserController instance, call .get() of Container with USER_CONTROLLER key.

const controller = container.get(USER_CONTROLLER);
controller.print();

// output
// UserController
// UserService

@inject decorator

export class UserController {
  constructor(
    @inject(USER_SERVICE)
    private userService: UserService
  ) {}
  // ...
}

With @inject decorator, decouple.js understand which dependent classes instances will be initialize and assign during create a new base class instance.

You can also use `@inject' decorator as property decorator like constructor parameter decorator as below.

export class UserController {
  @inject(USER_SERVICE)
  private userService: UserService;

  constructor() {}
  // ...
}

Binding Scopes

Specifies how long the created objects will live and how many times they should be created during the application lifecycle. Scopes can be defined by two way:

1. via .scope() function while class is introducing with.injectable()

container.injectable(USER_CONTROLLER, UserController).scope(BindingScope.SINGLETON);

2. via @injectable decorator which is above class definition

@injectable(BindingScope.SINGLETON)
export class UserController {
  // ...
}

One of scope definition methods is enough for a injectable class.

If two methods are used at the same time, the scope of method 1 will be valid.

If no scope is specified, the TRANSIENT scope will be valid.

Decouple.js supports two types of scope for now:

SINGLETON

Only one instance will be created during the application lifecycle and this same instance will be used by all dependent classes too.

TRANSIENT

A new instance will be created for each need of the class instance.

Example Implementation

• Decouple.js Implementation Example With Express.js

Next Features

1. express.js middleware support.
2. BindingScope.REQUEST support

License

Copyright © 2022 Abdulkadir Dede.

This project is licensed under the MIT License - see the LICENSE file for details.