Why Node.js crashes with Headers already sent Error when handling errors in Express

I'm using Express to create an API endpoint for user registration. The problem is, whenever I send a request that will initiate an error to that API endpoint, my node.js server crashes and gives me the following message:

node:internal/errors:491
[1]     ErrorCaptureStackTrace(err);
[1]     ^
[1]
[1] Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent 
to the client
[1]     at new NodeError (node:internal/errors:400:5)
[1]     at ServerResponse.setHeader (node:_http_outgoing:663:11)
[1]     at ServerResponse.header (D:\...\node_modules\express\lib\response.js:794:10)
[1]     at ServerResponse.send (D:\...\node_modul

So, the node.js server crashes whenever is sending an error (fail) response, but when it's sending success response it doesn't crash. So I guess I'm not handling errors proper here?

What I'm doing wrong here? Here is my implementation:

const registerUser = async (req: Request, res: Response) => {
  try {
    const userData = createUserSchema.parse(req.body) as User;

    const salt = await bcrypt.genSalt(10);
    const hashedPassword = await bcrypt.hash(userData.password, salt);

    const user = await db.user.create({
      data: {
        ...userData,
        password: hashedPassword,
      },
    });

    return res.status(201).json({
      status: 'success',
      data: { name: user.name, email: user.email },
    });
  } catch (error) {
    if (error instanceof z.ZodError) {
      return res.status(422).json({
        status: 'fail',
        message: error.issues,
      });
    } else if (error instanceof Prisma.PrismaClientKnownRequestError) {
      if (error.code === 'P2002') {
        return res.status(409).json({
          status: 'fail',
          message: 'Email address is already in use',
        });
      }
    }

    return res.status(500).json({
      status: 'fail',
      message: 'Something went wrong',
    });
  }
};

I've tried to return error only for one case to see if these responses are conflicting but even if I have only one response, node.js server crashes.

This error occurs because you are trying to set the response headers after they have already been sent to the client. In Express, you cannot set response headers after sending a response body part. This error occurs when you try to send an error (fail) response after you have already sent a response body part or a success response.

To fix this, make sure you're handling errors appropriately in your code. Make sure you don't send more than one response to the client for a single request. You can use the Express Error Handling Middleware to catch errors and send an appropriate response to the client without throwing an "ERR_HTTP_HEADERS_SENT" error.

Try with middleware like this:

app.use((err, req, res, next) => {
console.error(err);
res.status(500).json({
status: 'fail',
message: 'Something went wrong',
});
});

https://expressjs.com/en/guide/using-middleware.html

Using express middlware will save you a lot of effort