Why does `connectOverCDP()` work in Node.js but fail in Bun with `ConnectionRefused`?

General Discussions
1

I’m trying to use Playwright’s connectOverCDP() to attach to an existing Chrome instance in debug mode on my M1 Mac. My setup works fine with Node.js, but using Bun I get the following error:

ConnectionRefused: overCDP: Unable to connect. Is the computer able to access the url?
Call log:
  - <ws preparing> retrieving websocket url from http://localhost:9222

Here’s my code:

import { chromium } from 'playwright';

const browser = await chromium.connectOverCDP('http://localhost:9222');
const defaultContext = browser.contexts()[0];
const page = await defaultContext.newPage();
await page.goto('https://google.com');
await page.waitForTimeout(5000);
await browser.close();

I launch Chrome with:

/Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome \
--remote-debugging-port=9222 --no-first-run --no-default-browser-check \
--user-data-dir=chrome-user-data-dir --profile-directory=Default

How can I fix it so I can connect to the Chrome instance using Bun?

2

Playwright’s connectOverCDP() starts by requesting the DevTools WebSocket URL from http://localhost:9222/json/version.

In Node.js, this works fine because Node has a fully standard HTTP stack.

Bun’s built-in fetch and HTTP client currently have some differences in handling localhost, redirects, or non-200 responses.

If the request to http://localhost:9222/json/version fails, Playwright will throw ConnectionRefused.

Check manually:

curl http://localhost:9222/json/version

If this works, Node can fetch it.

In Bun, fetch(‘http://localhost:9222/json/version’) might fail due to Bun’s DNS or CORS restrictions.

3

On M1 Macs, Bun sometimes runs with sandboxing that prevents connecting to certain ports on localhost.

Node does not have this restriction.

Try running Bun with explicit network permissions:

bun --allow-net your-script.js

4

ConnectOverCDP() accepts a WebSocket URL too.

You can fetch it via Node or curl first:

curl http://localhost:9222/json/version

You’ll see something like:

{
  "webSocketDebuggerUrl": "ws://localhost:9222/devtools/browser/abcd1234"
}

Then, in Bun:

import { chromium } from 'playwright';

const browser = await chromium.connectOverCDP('ws://localhost:9222/devtools/browser/abcd1234');
const page = await browser.contexts()[0].newPage();
await page.goto('https://google.com');
await browser.close();

:white_check_mark: Using the WebSocket URL bypasses Bun’s HTTP fetch, which is likely the part that fails.