Watt Quick Start

Welcome to your first steps with Platformatic Watt, the Node.js Application Server. This guide will help you set up and run an application composed of the following stack:

• Next.js frontend, to render our frontend
• Generic node:http createServer, to showcase how to add an existing Node.js app
• Platformatic Composer, to coordinate/expose them all.

note

In this guide, we will use Next.js as our frontend framework, but you can also use Astro, or Remix. We plan to expand the list of supported frameworks in the future.

Prerequisites

Before starting, ensure you have the following installed:

• Node.js (v20.16.0+ or v22.3.0+)
• npm (v10 or higher)
• A code editor, (e.g., Visual Studio Code)

Set up Watt

npx wattpm@latest init

Which will output:

Hello YOUR_NAME, welcome to Watt 2.70.1!
? Where would you like to create your project? .
? Which kind of service do you want to create? @platformatic/service
✔ Installing @platformatic/service@^2.70.1 using npm ...
? What is the name of the service? my-app
? Do you want to create another service? no
? Do you want to use TypeScript? no
? What port do you want to use? 3042

Dependencies are going to be installed. Your application is located in web/my-app. The watt.json file is automatically created in the my-app folder, and the package.json file includes a start script and @platformatic/node as a dependency.

Add your first Node.js application to Watt

By choosing the @platformatic/node service, you have already created your nodejs app.

This file is created as your nodejs app:

import { createServer } from 'node:http'

export function create() {
  return createServer((req, res) => {
    res.writeHead(200, { 'content-type': 'application/json', connection: 'close' })
    res.end(JSON.stringify({ hello: 'world' }))
  })
}

note

In this example, we are using the built-in node:http module to create a simple HTTP server that responds with a JSON object containing a counter. You can see that we are returning a build function that creates the server. This server will be run by Watt when the application starts in its own worker thread.

You can also use Express, Fastify, Koa or any other Node.js framework.

Start your Watt server

Run the following command in the root of project to start your Watt server:

npm start

This will internally run wattpm start and start your Watt server.

note

running npm run start at the root directory is running the watt server. if you run npm run start at the service directory(in this case web/my-app) it is running that single service via this command from the service package.json script: start-platformatic-node

If you want to have a "watch mode" to automatically restart the server when you make changes, you can run this command in the root directory:

npm run dev

Which will run wattpm dev and start your Watt server in watch mode.

Your first Watt server is now live! 🌟 You can test it with:

curl http://localhost:3042

Add a Platformatic Composer to run multiple apps

Inside my-app, let's create a new Platformatic Composer

npx wattpm create

This will output:

Hello Matteo Collina, welcome to Platformatic 2.64.0
Using existing configuration ...
? Which kind of service do you want to create? @platformatic/composer
? What is the name of the service? composer
? Do you want to create another service? no
? Which service should be exposed? composer
? Do you want to use TypeScript? no
[16:06:50] INFO: /Users/matteo/tmp/my-app/.env written!
[16:06:50] INFO: /Users/matteo/tmp/my-app/.env.sample written!
[16:06:50] INFO: /Users/matteo/tmp/my-app/web/composer/package.json written!
[16:06:50] INFO: /Users/matteo/tmp/my-app/web/composer/platformatic.json written!
[16:06:50] INFO: /Users/matteo/tmp/my-app/web/composer/.gitignore written!
[16:06:50] INFO: /Users/matteo/tmp/my-app/web/composer/global.d.ts written!
[16:06:50] INFO: /Users/matteo/tmp/my-app/web/composer/README.md written!
[16:06:50] INFO: Installing dependencies for the application using npm ...
[16:06:50] INFO: Installing dependencies for the service composer using npm ...
[16:06:52] INFO: Project created successfully, executing post-install actions...
[16:06:52] INFO: You are all set! Run `npm start` to start your project.

Start your Watt server again:

You can run these commands in the root directory:

npm start

If you want to have a "watch mode" to automatically restart the server when you make changes, you can run this command in the root directory:

npm run dev

Which will run wattpm dev and start your Watt server in watch mode.

Then, you can test it with:

curl http://localhost:3042/node

note

You can customize how the various services are exposed by changing web/composer/platformatic.json. Here is the equivalent of the default configuration when exposing a Node.js application:

{
  "$schema": "https://schemas.platformatic.dev/@platformatic/composer/2.0.0.json",
  "composer": {
    "services": [{
      "id": "node",
      "proxy": {
        "prefix": "/node"
      }
    }],
    "refreshTimeout": 1000
  },
  "watch": true
}

Add a Next.js application to Watt

Inside my-app, let's create a new Next.js app:

npx create-next-app@latest web/next

Which will output:

✔ Would you like to use TypeScript? … No
✔ Would you like to use ESLint? … No
✔ Would you like to use Tailwind CSS? … No
✔ Would you like to use `src/` directory? … Yes
✔ Would you like to use App Router? (recommended) … Yes
✔ Would you like to customize the default import alias (@/*)? … No
Creating a new Next.js app in /Users/matteo/tmp/my-app/web/next.

Using npm.

Initializing project with template: app


Installing dependencies:
- react
- react-dom
- next


added 18 packages in 4s

195 packages are looking for funding
  run `npm fund` for details
Success! Created next at /Users/matteo/tmp/my-app/web/next

Then, let's import it to our watt server:

wattpm import web/next

We should also install the additional dependencies with:

npm i

Then, we need to tell Watt to expose our next server on /next by modifying web/next/watt.json:

{
  "$schema": "https://schemas.platformatic.dev/@platformatic/next/2.0.0.json",
  "application": {
    "basePath": "/next"
  }
}

You can run npm run dev to start your Watt server in dev/watch mode, which in turn will start Next.js in development mode.

Then, you can test it by opening your browser at http://localhost:3042/next.

note

In this example, we are exposing the Next.js app at /next and the Node.js app at /node. You can change the paths to suit your needs. Make sure to alter the basePath in web/next/watt.json and the prefix in web/composer/platformatic.json accordingly if you customize it.

fetch the data from the Node.js app in the Next.js app

Replace web/next/src/app/page.js, with the following code:

import styles from "./page.module.css";

export default async function Home() {
  const { content } = await (await fetch("http://node.plt.local", { cache: 'no-store' })).json();
  return (
    <div className={styles.page}>
      <main className={styles.main}>
        ${content}
      </main>
    </div>
  );
}

This will fetch the data from the Node.js app and display it in the Next.js app. Note that it uses the node.plt.local hostname, which is the internal hostname for the node service. This domain name would not work outside of a Watt or Platformatic environment.

note

By default Next.js caches all fetch() requests. The { cache: 'no-store' } option is used to disable caching, so that you can see the counter incrementing.

Launch it with: npm run dev.

You can now test it by opening your browser at http://localhost:3042/next.

Build and Production mode

To create a build for production, you can run wattpm build, which is exposed as npm script:

npm run build

Which will in turn create a build for Next.js and for the Node.js app (in case that is needed).

To run the server in production mode, you can run:

npm run start

which will call wattpm start.

Debug individual services with Chrome DevTools

You can debug your Watt server with Chrome DevTools by running:

npm run start -- --inspect

This will start an inspector instance in each service, and you can connect to it with Chrome DevTools. Open chrome://inspect in Chrome, and you will see the services listed there.

Then, you can click on inspect to open the DevTools for that service.

Debug individual services with VS Code

You can debug the code of individual Watt services directly in VS Code.

To run the debugger in VS Code:

• add a breakpoint in your Watt service code
• open the Command Palette (Ctrl+Shift+P on Windows, CMD+Shift+P on Mac)
• search Debug: Toggle Auto Attach, then select Always from the list of options
• run watt with npm run dev
• you should now see in your shell a log that confirms that the debugger is listening

Debugger listening on ws://127.0.0.1:62807/6132054c-766e-4d86-a716-f634118275ed
For help, see: https://nodejs.org/en/docs/inspector
Debugger attached.

• do a request to your service, to trigger the breakpoint code, and use VS Code to debug it as by the following screenshot