DIME: Dependency injection made easy

Dime is an extremely lightweight node.js library for dependency injection.

What is dependency injection?

Dependency injection is a way to decouple the pieces of your code; that is, separate the definition and implementation of your code.

Why should you use dependency injection?

Here’s an example of an ItemsWidget which receives its data from AmazonItemsService.

// Without Dime 👎
import { AmazonItemsService } from './amazon-items-service';

class ItemsWidget {
    constructor(private itemsService: AmazonItemsService) {}

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

// Display the widget
const widget = new ItemsWidget(new AmazonItemsService());
widget.render();

This looks fine at first glance, but what if at some point you decided to get your items from eBay instead of Amazon? Then you would have to replace AmazonItemsService with EbayItemsService. This isn’t a big deal in the simple example above, but if ItemsWidget was used in several places throughout the code, this would be more difficult. As a project gets larger, it becomes impossible to maintain a codebase like this, and that’s where Dime comes in.

// With Dime 👍
import { ItemsService } from './items-service';
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 Amazon implementation
});

Dime.configure().withPackages(appPackage).lazy().load();

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

In this version of the code, ItemsService is an interface. Using Dime allows you to abstract away the implementation details of ItemsService. Here, if you wanted to use EbayItemsService instead, you would only need to change the code in one place, no matter how many times you used ItemsWidget.