Object Modeling and Domain Types

Use interfaces, type aliases, readonly data, branded IDs, and state types to model complex domains.

42 min

3 sections

interfaces

readonly

brands

domain

01. Interfaces for Extensible Object Contracts

Section 1 of 3

Interfaces are a good fit for object contracts that may be implemented by classes or extended by consumers. Type aliases are better for unions, intersections, and computed types. In app code, choose readability over ideology.

typescript

interface QueuePublisher {
  publish(topic: string, message: unknown): Promise<void>;
}

class BillingPublisher implements QueuePublisher {
  async publish(topic: string, message: unknown): Promise<void> {
    console.log("publish", topic, message);
  }
}

type BillingTopic = "invoice.created" | "payment.failed";

Runtime Validation and Schema Boundaries

Generics for Reusable Enterprise Code

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