useSubscription()

The useSubscription hook can be used to subscribe to a subscription procedure on the server.

Signature

Options

tip

• If you need to set any options but don't want to pass any input, you can pass undefined instead.
• If you pass skipToken from @tanstack/react-query, the subscription will be paused.
• Have a look at our SSE example for a complete example of how to use subscriptions

tsx
function useSubscription<TOutput, TError>(
  input: TInput | SkipToken,
  opts?: UseTRPCSubscriptionOptions<TOutput, TError>
): TRPCSubscriptionResult<TOutput, TError>;
interface UseTRPCSubscriptionOptions<TOutput, TError> {
  /**
   * Callback invoked when the subscription starts.
   */
  onStarted?: () => void;
  /**
   * Callback invoked when new data is received from the subscription.
   * @param data - The data received.
   */
  onData?: (data: TOutput) => void;
  /**
   * Callback invoked when an **unrecoverable error** occurs and the subscription is stopped.
   */
  onError?: (error: TError) => void;
  /**
   * @deprecated Use a `skipToken` from `@tanstack/react-query` instead.
   * This will be removed in a future version.
   */
  enabled?: boolean;
}

tsx
function useSubscription<TOutput, TError>(
  input: TInput | SkipToken,
  opts?: UseTRPCSubscriptionOptions<TOutput, TError>
): TRPCSubscriptionResult<TOutput, TError>;
interface UseTRPCSubscriptionOptions<TOutput, TError> {
  /**
   * Callback invoked when the subscription starts.
   */
  onStarted?: () => void;
  /**
   * Callback invoked when new data is received from the subscription.
   * @param data - The data received.
   */
  onData?: (data: TOutput) => void;
  /**
   * Callback invoked when an **unrecoverable error** occurs and the subscription is stopped.
   */
  onError?: (error: TError) => void;
  /**
   * @deprecated Use a `skipToken` from `@tanstack/react-query` instead.
   * This will be removed in a future version.
   */
  enabled?: boolean;
}

Return type

ts
type TRPCSubscriptionResult<TOutput, TError> = {
  /**
   * The current status of the subscription.
   * Will be one of: `'idle'`, `'connecting'`, `'pending'`, or `'error'`.
   *
   * - `idle`: subscription is disabled
   * - `connecting`: trying to establish a connection
   * - `pending`: connected to the server, receiving data
   * - `error`: an error occurred and the subscription is stopped
   */
  status: 'idle' | 'connecting' | 'pending' | 'error';
  /**
   * The last data received from the subscription.
   */
  data: TOutput | undefined;
  /**
   * The last error received - will be `null` whenever the status is `'pending'` or `'idle'`
   * - has a value only when the status is `'error'`
   * - *may* have a value when the status is `'connecting'`
   */
  error: TRPCClientError | null;
  /**
   * Function to reset the subscription.
   */
  reset: () => void;
};

ts
type TRPCSubscriptionResult<TOutput, TError> = {
  /**
   * The current status of the subscription.
   * Will be one of: `'idle'`, `'connecting'`, `'pending'`, or `'error'`.
   *
   * - `idle`: subscription is disabled
   * - `connecting`: trying to establish a connection
   * - `pending`: connected to the server, receiving data
   * - `error`: an error occurred and the subscription is stopped
   */
  status: 'idle' | 'connecting' | 'pending' | 'error';
  /**
   * The last data received from the subscription.
   */
  data: TOutput | undefined;
  /**
   * The last error received - will be `null` whenever the status is `'pending'` or `'idle'`
   * - has a value only when the status is `'error'`
   * - *may* have a value when the status is `'connecting'`
   */
  error: TRPCClientError | null;
  /**
   * Function to reset the subscription.
   */
  reset: () => void;
};

Example

components/MyComponent.tsx
tsx
import { trpc } from '../utils/trpc';
export function MyComponent() {
  const [numbers, setNumbers] = React.useState<number[]>([]);
  const result = trpc.onNumber.useSubscription(undefined, {
    onData: (num) => {
      setNumbers((prev) => [...prev, num]);
    },
  });
  return (
    <div>
      <h1>Subscription Example</h1>
      <p>
        {status}: <pre>{JSON.stringify(data, null, 2)}</pre>
      </p>
      <h2>Previous numbers:</h2>
      <ul>
        {numbers.map((num, i) => (
          <li key={i}>{num}</li>
        ))}
      </ul>
      {result.status === 'error' && (
        <button onClick={() => result.reset()}>
          Something went wrong - restart the subscription
        </button>
      )}
    </div>
  );
}

components/MyComponent.tsx
tsx
import { trpc } from '../utils/trpc';
export function MyComponent() {
  const [numbers, setNumbers] = React.useState<number[]>([]);
  const result = trpc.onNumber.useSubscription(undefined, {
    onData: (num) => {
      setNumbers((prev) => [...prev, num]);
    },
  });
  return (
    <div>
      <h1>Subscription Example</h1>
      <p>
        {status}: <pre>{JSON.stringify(data, null, 2)}</pre>
      </p>
      <h2>Previous numbers:</h2>
      <ul>
        {numbers.map((num, i) => (
          <li key={i}>{num}</li>
        ))}
      </ul>
      {result.status === 'error' && (
        <button onClick={() => result.reset()}>
          Something went wrong - restart the subscription
        </button>
      )}
    </div>
  );
}