Exiting Node Child Process After Processing Data Output

I'm using Node.js to spawn puppeteer in a separate process.

Here's that child process (it writes the websocket to the standard output stream):

// path: cp/index.js

(async () => {
  const browser = await puppeteer.launch();
  const wsEndpoint = browser.wsEndpoint();
  process.stdout.write(wsEndpoint);
})();

Within the main process, I'm connecting to the puppeteer instance using the websocket. Like so:

var cp = await spawn('node', ['./cp/index.js'], {
    detached: true,
    shell: true,
    cwd: __dirname,
});

cp.stdout.on('data', async (ws) => {
    let browser = await puppeteer.connect({ browserWSEndpoint: ws.toString() });
    // Do some processing.
    // Exit the child process.
});

But unfortunately, I'm unable to access the child process within the cp.on('data') callback, in order to exit after processing.

How can I get access to the websocket from my child process, connect in the main process, perform some asynchronous code, and then disconnect from the child process?