在 Node.js 中注入 Typescript 依赖项的更好方法？

Question

I'm working on a backend solution in Node.js and Express, using Typescript. I'm trying to do dependency injection similar to Angular, but lacking the @Injectable() decorator I'm doing this:

Dependency:

export class SomeDependency {
  public someMethod() {
    console.log('Some method is running');
  }
}

Parent:

import { SomeDependency } from './someDependency';

export class Whatever {

  constructor(
    private someDependency = new SomeDependency()
  ) {}

  public doSomething() {
    console.log('Look, I\'m doing something!');
    this.someDependency.someMethod();
  }
}

It works, but it may not be the best way. Any suggestions on how to improve it are appreciated.

On the other hand, what do you guys think: is it better to import dependencies like this, in the constructor, or create new instance every time, or most of the time? Like this:

import { SomeDependency } from './someDependency';

export class Whatever {

  public doSomething() {
    console.log('Look, I\'m doing something!');
    new someDependency().someMethod();
  }
}

As SomeDependency isn't a singleton, I wonder which one is less efficient: keeping an instance alive in the parent, or creating a new one every time, letting the garbage collector take care of it when the call finished.

Answer 1

your use case is absolutely correct. It is always a good practice to keep your modules as lightly coupled. So, in future you can switch between the implementation without touching the main logic but the Javascript or Typescript doesn't provide the dependency injection mechanism.

To achieve this you can use a library know as Inversify.

Inversify is powerful and lightweight inversion of control container for JavaScript & NodeJS. It implements IoC and allow us to inject dependencies, uncoupling our method from any implementation details

It give you the same functionality as we use in Angular like you can annotate the class with @Injectable() annotation and perform dependency injection.

For reference you can go to: https://www.linkedin.com/pulse/how-use-dependency-injection-nodejs-typescript-projects-ribeiro

Answer 2

You may want to look into Dime . It's a very simple library I made for dependency injection similar to Angular. There are more details on the Github page and the wiki . It's still in early development, so there might be bugs.

Example:

import { ItemsService } from './items-service'; // ItemsService is an interface
import { Inject } from '@coined/dime';

class ItemsWidget {
    @Inject()
    private itemsService: ItemsService;

    render() {
        this.itemsService.getItems().subscribe(items => {
            // ...
        })
    }
}

// Setup
const appPackage = new Package("App", {
    token: "itemsService",
    provideClass: AmazonItemsService // Use any implementation
});

Dime.mountPackages(appPackage);

// Run the application
const widget = new ItemsWidget();
widget.render();