# Nexus TypeScript Quickstart

> Build a Nexus Service that wraps an existing Temporal Workflow using the TypeScript SDK

> **Public Preview**

[Temporal Nexus](/evaluate/nexus) connects Temporal Applications within and across Namespaces using a Nexus Endpoint, a Nexus Service contract, and Nexus Operations. Build a Nexus Service that wraps an existing Temporal Workflow, then invoke it from a caller Workflow.

> **ℹ️ Info:**
> NEW TO NEXUS?
> This page will help you get a working sample running in TypeScript.
> To evaluate whether Nexus fits your use case, see the [evaluation guide](/evaluate/nexus) and to learn more about Nexus features, click [here](/nexus).

**Prerequisites:** Complete the [TypeScript SDK Quickstart](/develop/typescript/set-up-your-local-typescript) first.
You should have `activities.ts`, `workflows.ts`, `worker.ts`, and `client.ts` from that guide.

## What you'll build

You have `example` running in the `default` Namespace.
By the end of this guide:

1. A Nexus Service will expose `example` as an Operation.
2. A second Namespace will contain a Workflow that calls that Operation.
3. The caller Workflow will get back `"Hello, Temporal!"` — the same result, but across Namespaces.

## 1. Define the Nexus Service

Create a file called `service.ts` that defines the Nexus Service contract.

Creating a Nexus Service establishes the contract between your implementation and any callers.
It provides type safety when invoking Nexus Operations and ensures that Operation Handlers fulfill the contract.

`nexus.service()` declares a named service, and `nexus.operation<I, O>()` defines a typed operation.
The `example` Workflow returns `string`, so the operation output type is `string`.

```typescript
{`import * as nexus from 'nexus-rpc';

export interface MyInput {
    name: string;
}

export const sayHelloService = nexus.service('say-hello', {
    sayHello: nexus.operation<MyInput, string>(),
});`}
```

## 2. Define the Nexus Operation handlers

Create a file called `handler.ts` that implements the Nexus Operation handler.

Operation handlers contain the logic that runs when a caller invokes a Nexus Operation.

`WorkflowRunOperationHandler` creates an asynchronous Nexus Operation that starts a Workflow.
The handler bridges the Nexus `MyInput` interface to the `example` Workflow's `string` parameter by extracting `input.name`.

```typescript
{`import { randomUUID } from 'crypto';
import * as nexus from 'nexus-rpc';
import * as temporalNexus from '@temporalio/nexus';
import { sayHelloService, MyInput } from './service';
import { example } from './workflows';

export const sayHelloHandler = nexus.serviceHandler(sayHelloService, {
    sayHello: new temporalNexus.WorkflowRunOperationHandler<MyInput, string>(
      async (ctx, input: MyInput) => {
        return await temporalNexus.startWorkflow(ctx, example, {
          args: [input.name],
          workflowId: "say-hello-nexus-" + randomUUID(),

          // Task queue defaults to the task queue this Operation is handled on.
        });
      },
    ),
});`}
```

## 3. Register the Nexus Service handler in a Worker

Update your existing `worker.ts` to register the Nexus Service Handler.

A Worker will only poll for and process incoming Nexus requests if the Nexus Service Handlers are registered.
This is the same Worker concept used for Workflows and Activities.

The `nexusServices` parameter registers the handler so it can receive Nexus Operation requests.

```typescript
{`import { NativeConnection, Worker } from '@temporalio/worker';
import * as activities from './activities';
import { sayHelloHandler } from './handler';

async function run() {
    const connection = await NativeConnection.connect({
      address: 'localhost:7233',
    });
    try {
      const worker = await Worker.create({
        connection,
        namespace: 'default',
        taskQueue: 'hello-world',
        workflowsPath: require.resolve('./workflows'),
        activities,
        nexusServices: [sayHelloHandler],
      });
      await worker.run();
    } finally {
      await connection.close();
    }
}

run().catch((err) => {
    console.error(err);
    process.exit(1);
});`}
```

## 4. Develop the caller Workflow

Update your existing `workflows.ts` file with a Workflow which invokes the Nexus Operation.

The caller Workflow demonstrates the consumer side of Nexus.
Instead of importing handler code directly, the caller only depends on the Service contract.
This keeps the caller and handler decoupled so they can live in separate Namespaces, repositories, or even teams.

The `wf.createNexusServiceClient()` method creates a client bound to your Nexus Service and Endpoint.
`executeOperation` starts the operation and waits for the result.

```typescript
{`import { proxyActivities, createNexusServiceClient } from '@temporalio/workflow';
// Only import the activity types
import type * as activities from './activities';
import { sayHelloService } from './service';

const { greet } = proxyActivities<typeof activities>({
    startToCloseTimeout: '1 minute',
});

/** A workflow that simply calls an activity */
export async function example(name: string): Promise<string> {
    return await greet(name);
}

const NEXUS_ENDPOINT = 'my-nexus-endpoint-name';

export async function callerWorkflow(name: string): Promise<string> {
    const nexusClient = createNexusServiceClient({
      service: sayHelloService,
      endpoint: NEXUS_ENDPOINT,
    });
    return await nexusClient.executeOperation('sayHello', { name }, { scheduleToCloseTimeout: '10s' });
}
`}
```

## 5. Create the caller Namespace and Nexus Endpoint

Before running the application, create a caller Namespace and a Nexus Endpoint to route requests from the caller to the handler.
The handler uses the `default` Namespace that was created when you started the dev server.

Namespaces provide isolation between the caller and handler sides.
The Nexus Endpoint acts as a routing layer that connects the caller Namespace to the handler's target Namespace and Task Queue.
The endpoint name must match the variable defined in `caller.ts` from step 4.

Make sure your local Temporal dev server is running (`temporal server start-dev`).

```bash
temporal operator namespace create --namespace my-caller-namespace
```

```bash
{`temporal operator nexus endpoint create \\
  --name my-nexus-endpoint-name \\
  --target-namespace default \\
  --target-task-queue hello-world`}
```

## 6. Run and Verify

Create a file called `caller-starter.ts` to start the caller Worker and execute the Workflow.

This step brings everything together: the caller Worker hosts `callerWorkflow`, which uses the Nexus client to invoke `sayHello` on the handler side.
The full request flows from the caller Workflow, through the Nexus Endpoint, to the handler Worker running the `example` Workflow, and back to the caller.

**Run the application:**

1. Start the handler Worker in one terminal:

```bash
npx ts-node src/worker.ts
```

2. Run the caller in another terminal:

```bash
npx ts-node src/caller-starter.ts
```

You should see:

```
Workflow result: Hello, Temporal!
```

Open the [Temporal Web UI](http://localhost:8233) and find the `callerWorkflow` execution.
You should see `NexusOperationScheduled`, `NexusOperationStarted`, and `NexusOperationCompleted` events in the Event history.

```typescript
{`import { randomUUID } from 'crypto';
import { Connection, Client } from '@temporalio/client';
import { NativeConnection, Worker } from '@temporalio/worker';
import { callerWorkflow } from './workflows';

const CALLER_TASK_QUEUE = 'my-caller-task-queue';
const NAMESPACE = 'my-caller-namespace';

async function main() {
    const clientConnection = await Connection.connect({
      address: 'localhost:7233',
    });
    const client = new Client({
      connection: clientConnection,
      namespace: NAMESPACE,
    });

    const workerConnection = await NativeConnection.connect({
      address: 'localhost:7233',
    });
    try {
      const worker = await Worker.create({
        connection: workerConnection,
        namespace: NAMESPACE,
        taskQueue: CALLER_TASK_QUEUE,
        workflowsPath: require.resolve('./workflows'),
      });

      await worker.runUntil(async () => {
        const result = await client.workflow.execute(callerWorkflow, {
          args: ['Temporal'],
          workflowId: \`caller-workflow-\${randomUUID()}\`,
          taskQueue: CALLER_TASK_QUEUE,
        });
        console.log('Workflow result:', result);
      });
    } finally {
      await workerConnection.close();
    }
}

main().catch((err) => {
    console.error(err);
    process.exit(1);
});`}
```

## Next Steps

Now that you have a working Nexus Service, here are some resources to deepen your understanding:

- **[TypeScript Nexus Feature Guide](/develop/typescript/nexus)**: Covers synchronous and asynchronous Operations, error handling, cancellation, and cross-Namespace calls.
- **[Nexus Operations](/nexus/operations)**: The full Operation lifecycle, including retries, timeouts, and execution semantics.
- **[Nexus Services](/nexus/services)**: Designing Service contracts and registering multiple Services per Worker.
- **[Nexus Patterns](/nexus/patterns)**: Comparing the collocated and router-queue deployment patterns.
- **[Error Handling in Nexus](/nexus/error-handling)**: Handling retryable and non-retryable errors across caller and handler boundaries.
- **[Execution Debugging](/nexus/execution-debugging)**: Bi-directional linking and OpenTelemetry tracing for debugging Nexus calls.
- **[Nexus Endpoints](/nexus/endpoints)**: Managing Endpoints and understanding how they route requests.
- **[Temporal Nexus on Temporal Cloud](/cloud/nexus)**: Deploying Nexus in a production Temporal Cloud environment with built-in access controls and multi-region connectivity.