Local Link

localLink is a terminating link that allows you to make tRPC procedure calls directly in your application without going through HTTP.

:::info We have prefixed this as unstable_ as it's a new API, but you're safe to use it! Read more. :::

Usage

// @filename: server.ts
import { initTRPC } from '@trpc/server';
const t = initTRPC.create();
export const appRouter = t.router({});
export type AppRouter = typeof appRouter;

// @filename: client.ts
// ---cut---
import { createTRPCClient, unstable_localLink } from '@trpc/client';
import type { AppRouter } from './server';
import { appRouter } from './server';

const client = createTRPCClient<AppRouter>({
  links: [
    unstable_localLink({
      router: appRouter,
      createContext: async () => {
        // Create your context here
        return {};
      },
      onError: (opts) => {
        // Log errors here, similarly to how you would in an API route
        console.error('Error:', opts.error);
      },
    }),
  ],
});

Features

• Direct procedure calls without HTTP overhead
• Full support for queries, mutations, and subscriptions
• Automatic error handling and transformation
• Support for abort signals
• Type-safe context creation

Options

The localLink accepts the following options:

type AnyRouter = any;
type inferRouterContext<T> = any;
type inferClientTypes<T> = any;
type ErrorHandlerOptions<T> = any;
type TransformerOptions<T> = {};
// ---cut---
type LocalLinkOptions<TRouter extends AnyRouter> = {
  router: TRouter;
  createContext: () => Promise<inferRouterContext<TRouter>>;
  onError?: (opts: ErrorHandlerOptions<inferRouterContext<TRouter>>) => void;
} & TransformerOptions<inferClientTypes<TRouter>>;

router

The tRPC router instance to use for procedure calls.

createContext

A function that creates the context for each procedure call. This is called for each request and should return a promise that resolves to the context object.

onError

An optional error handler that is called when an error occurs during a procedure call. It receives the error, operation type, path, input, and context.

transformer

Optional input/output transformers for serialization/deserialization of data.

Notes

• It's recommended to use this link in scenarios where you need direct procedure calls without HTTP
• For most client-side applications, you should use the httpLink or other HTTP-based links instead
• The link supports all tRPC features including queries, mutations, and subscriptions
• Error handling and transformation are handled automatically, just like with HTTP-based links