To define the Domain Model in Node.js, we need to understand the key concepts of DDD. These concepts include:

Entities: Objects that have an identity and are unique within the system. Examples of entities in an e-commerce system might include Customers, Products, and Orders.

Value Objects: Objects that represent a concept, but do not have an identity of their own. Examples of value objects in an e-commerce system might include Money, Address, and Quantity.

Aggregates: Clusters of related objects that are treated as a single unit of work. Aggregates are used to enforce consistency and invariants within the system. Examples of aggregates in an e-commerce system might include Carts, Orders, and Payments.

Domain Services: Services that perform complex operations or coordinate interactions between entities and aggregates. Examples of domain services in an e-commerce system might include PaymentGateway and ShippingService.

Here is an example of how we can define the Domain Model for an e-commerce system in Node.js: