DDD

Software engineering practices for Domain Driven Design made in JavaScript/TypeScript

Inspired by (Rus): https://www.youtube.com/watch?v=cT-VOwWjJJs&t=2949s
Presentation (Rus): https://drive.google.com/file/d/1tsptt7aRNJ3tWsGXHNhbJiRhHF_DDupo/view

All examples are provided in JavaScript/TypeScript, considering the runtime environment as NodeJS

Keypoints

1. Clean architecture

On the image below we can see the distinct segregation of business domain entities and surrounding layers of its accessors, which are:

• Application (use cases)
• Periphery interface adapters (controllers, gateways, Presenters)
• Infrastructure (DB, clients, external interfaces)

This separation gives to the Domain Drived Design powerfull abstraction, reusability, maintainability characteristics based on isolating the core of a business model entities, i.e. the domain

2. Entities

We may think about these domain particulars named entities as of different sorts of interfaces. Let's take a quick look on some example, demonstrating the core of such domain model as digital assets e-commerce platform.

/**
 * @entity Plain digital asset
 */
interface IDigitalAsset {
    name: string,
    description: string,
    type: TDigitalAssetsTypes,
}

/**
 * @entity Digital asset owned by a user (seller | customer)
 */
interface IOwnerDigitalAsset {
    asset: IDigitalAsset,
    owner: IOwner,
}

/**
 * @entity Platform user (seller | customer) with at least one digital asset
 */
interface IOwner {
    nickName: string,
    firstName: string,
    secondName?: string,
    assets: IOwnerDigitalAsset[],
}

type TDigitalAssetsTypes<T> = T
    | SubscritionType
    | ProgrammKeyType
    // ...

It's quite clear that even looking only at these interfaces we certainly could tell what are the business entities of business rules in considered domain.

Here we can clearly see the business model:

• There're some digital assets like subsctiptions and programm keys, which sellers have and sell them to customers
• Both sellers and customers may own some digital assets