# Async Error Handling — Express.js Fundamentals: Routing, Middleware and APIs

Source: https://www.skillbyai.com/en/expressjs/ex-async-errors

> Forward errors from async handlers with next, wrappers or Express 5's automatic promise handling.

## The gotcha

In Express 4, a rejected promise inside an `async` route handler does **not** reach your error middleware; it must be forwarded with `next(err)`. Express 5 (now the default on npm) forwards it automatically.

## Catch and forward

Wrap the body in `try/catch` and call `next(err)` — or use a small helper to avoid repeating it.

```javascript
const asyncHandler = (fn) => (req, res, next) =>
  Promise.resolve(fn(req, res, next)).catch(next);

app.get('/users/:id', asyncHandler(async (req, res) => {
  const user = await db.users.findById(req.params.id);
  if (!user) {
    const err = new Error('User not found');
    err.status = 404;
    throw err;
  }
  res.json(user);
}));
```

## Express 5 fixes this

Express 5 automatically forwards rejected promises from async handlers to `next(err)` — the wrapper becomes unnecessary once you're on Express 5.