How to handle async route handlers without crashing Express

Async Error Handling in Express

Express 4 does not catch promise rejections automatically. An unhandled rejection in an async route handler crashes the process or hangs the request.

The problem

// This will crash if fetchData() throws
app.get('/data', async (req, res) => {
  const data = await fetchData(); // unhandled rejection
  res.json(data);
});

Option 1 — try/catch every handler

app.get('/data', async (req, res, next) => {
  try {
    const data = await fetchData();
    res.json(data);
  } catch (err) {
    next(err); // pass to error handler
  }
});

Option 2 — asyncHandler wrapper (DRY)

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

// Usage — no try/catch needed
app.get('/data', asyncHandler(async (req, res) => {
  const data = await fetchData();
  res.json(data);
}));

app.post('/users', asyncHandler(async (req, res) => {
  const user = await createUser(req.body);
  res.status(201).json(user);
}));

The asyncHandler wrapper is ~2 lines but eliminates try/catch boilerplate across every async route. Express 5 (released stable) handles this natively — but until your app uses Express 5, this wrapper is essential.