Centralized Vs Component specific type definitions in TS projects

TypeScript is fast becoming todays mainstream approach to build modern web applications. Using typescript provides the opportunity for developers to build applications that are easily maintainable, reusable and scalable. However, two primary approaches exist in managing types in our applications; centralized and specific type definitions. Understanding when to use each can significantly impact your projects maintainability.

Centralized Type Definitions

Centralized types are defined in a common location, usually, a folder called types, and adding a file with a .ts extension, which can be shared across the project. This usually have a single truth source, and it makes an ease of use and maintainability. Also, reduces duplication of types that can easily be shared even in different usage cases. They're ideal for:

1. Utility types

2. Global state types

3. API contract

Specific Type Definitions

Specific types are defined close to where they're used, often in the same file. Using specific type definitions in your project can improve code readability, streamlined coupling and ease understanding of component requirements. However, they may at times be unnecessary duplication of types. They're suitable for:

1. Component and module-specific props and state

2. Local helper types

3. Function-specific parameter and return types

Deciding on which approach to use can depends on your project type. Developers often are expected to combine types based on need or necessity. You can use centralized types for shared, stable concepts and use specific types for localized, and frequently changing structures. A few things you can consider include:

• Code re-usability

• Scope of project

• Code maintainability

Practical Example

// /types/centralized.ts
export interface User {
  id: string;
  name: string;
  email: string;
}

// userService.ts
import { User } from './types/centralized';

interface CreateUserData {
  name: string;
  email: string;
  password: string;
}

class UserService {
  async createUser(data: CreateUserData): Promise<User> {
    // Implementation
  }
}

// userComponent.ts
import { User } from './types/centralized';

interface UserComponentProps {
  user: User;
  onUpdate: (user: User) => void;
}

function UserComponent({ user, onUpdate }: UserComponentProps) {
  // Component implementation
}

In this example, User is centralized due to its shared nature, while CreateUserData and UserComponentProps are specific to their respective contexts.

Conclusion

In TypeScript, effective type organization involves balancing centralized and specific definitions. By understanding the trade-offs and applying the right approach in each context, you can write more maintainable and scalable TypeScript codes. The best solution often combines both strategies, and adapting it to your project.