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tRPC End-to-End Type Safe APIs · Lesson

Code Sharing and Reusability

Learn strategies for maximizing code reuse between client and server, especially for types and utilities.

Code Sharing and Reusability is a free tRPC End-to-End Type Safe APIs lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the tRPC End-to-End Type Safe APIs learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Why Share Code?

In a tRPC monorepo, you often have multiple applications (client, server, admin panel) that need to interact with the same data structures or perform similar tasks.

Code sharing is a powerful technique that helps reduce duplication, ensure consistency, and improve the overall maintainability of your project.

Types Across Client & Server

One of tRPC's biggest advantages is end-to-end type safety. This means your frontend automatically knows the types of data your backend sends and receives.

This magic relies heavily on sharing TypeScript types and interfaces between your client and server applications.

Defining a Shared Type

Let's create a simple User interface in a dedicated packages/types directory. This package will be imported by both your server and client.

/* packages/types/src/user.ts */
export interface User {
  id: string;
  name: string;
  email: string;
}

Server-side Shared Types

Now, we can use this User type to define the expected output of a tRPC query on our backend. This ensures the data sent from the server strictly adheres to the User structure.

/* packages/server/src/router/user.ts */
import { publicProcedure, router } from '../trpc';
import { User } from '@my-monorepo/types'; // Import shared type

export const userRouter = router({
  getUsers: publicProcedure
    .query(async () => {
      const users: User[] = [
        { id: '1', name: 'Alice', email: 'alice@example.com' },
        { id: '2', name: 'Bob', email: 'bob@example.com' },
      ];
      return users; // tRPC infers return type as User[]
    }),
});

Client-side Shared Types

On the client, tRPC automatically infers the types for users based on the server's definition. While explicit import isn't always needed for inference, it improves clarity and allows you to use the type for local client-side state or props.

/* packages/client/src/components/UserList.tsx */
import { trpc } from '../utils/trpc';
import { User } from '@my-monorepo/types'; // Optional, but good practice

function UserList() {
  const { data: users, isLoading } = trpc.user.getUsers.useQuery();

  if (isLoading) return <div>Loading users...</div>;

  return (
    <div>
      {users?.map((user: User) => ( // 'user' is typed as User
        <p key={user.id}>{user.name} ({user.email})</p>
      ))}
    </div>
  );
}

Sharing Utility Functions

Beyond types, many other pieces of code can be shared. This includes common utility functions, constants, validation schemas (like Zod schemas), or even shared UI components if you're using a component library.

Sharing these helps maintain a consistent user experience and reduces redundant code across your applications.

Creating a Utility Package

Let's create a simple utility function in a packages/utils directory that formats a full name. We'll also include a shared constant.

/* packages/utils/src/format.ts */
export function formatFullName(firstName: string, lastName: string): string {
  return `${firstName} ${lastName}`;
}

export const APP_NAME = 'CoddyKit Learn'; // Example constant

Server-side Utilities

You can import and use these shared utility functions directly in your tRPC backend procedures. This ensures consistent logic, regardless of whether it's triggered by an API call or internal server processes.

/* packages/server/src/router/profile.ts */
import { publicProcedure, router } from '../trpc';
import { formatFullName } from '@my-monorepo/utils'; // Import shared utility
import { z } from 'zod'; // Assuming Zod is configured

export const profileRouter = router({
  getUserProfile: publicProcedure
    .input(z.object({ firstName: z.string(), lastName: z.string() }))
    .query(({ input }) => {
      const fullName = formatFullName(input.firstName, input.lastName);
      return { greeting: `Hello, ${fullName}!` };
    }),
});

Client-side Utilities

Similarly, your client-side application can import and use the exact same utility functions and constants. This guarantees that calculations or displayed text are consistent with the server's logic.

/* packages/client/src/components/Greeting.tsx */
import { formatFullName, APP_NAME } from '@my-monorepo/utils'; // Import shared utility

function Greeting() {
  const firstName = "Jane";
  const lastName = "Doe";
  const formattedName = formatFullName(firstName, lastName);

  return (
    <div>
      <h1>Welcome to {APP_NAME}!</h1>
      <p>User: {formattedName}</p>
    </div>
  );
}

Best Practices for Shared Code

  • Granularity: Create small, focused shared packages (e.g., types, utils, ui).
  • Dependencies: Shared packages should have minimal external dependencies to avoid bloating other apps.
  • Avoid Circular Deps: Be careful not to create circular dependencies between shared packages or between app and shared packages.
  • Testing: Test shared code thoroughly, as changes can affect multiple applications.

Shared Code Benefits

Which of the following are primary benefits of sharing types and utility functions between client and server in a tRPC monorepo?

Recap: Sharing is Caring!

We explored how sharing types and utility functions in a tRPC monorepo is key to maximizing efficiency. This approach reduces duplication, enhances type safety, and improves overall maintainability across your client and server applications. By structuring your project carefully, you can build robust and consistent full-stack applications.

Frequently asked questions

Is the “Code Sharing and Reusability” lesson free?

Yes — the full text of “Code Sharing and Reusability” is free to read here on the web, and the tRPC End-to-End Type Safe APIs course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the tRPC End-to-End Type Safe APIs course, upgrade to CoddyKit PRO.

What will I learn in “Code Sharing and Reusability”?

Learn strategies for maximizing code reuse between client and server, especially for types and utilities. You practise tRPC End-to-End Type Safe APIs with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start tRPC End-to-End Type Safe APIs?

No prior experience is required. tRPC End-to-End Type Safe APIs on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Code Sharing and Reusability” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this tRPC End-to-End Type Safe APIs lesson?

Yes. Every tRPC End-to-End Type Safe APIs lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Setting Up a tRPC Monorepo
  2. Code Sharing and Reusability
  3. Extending tRPC Functionality
  4. Versioning and Publishing Shared tRPC Packages
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