Q15: How are asynchronous errors handled in Express 4 vs Express 5?
In Express 4, unhandled promise rejections inside async route handlers bypass Express error handling and crash the Node process unless explicitly caught or passed to next(err).
In Express 5, route handlers returning rejected Promises automatically forward the caught error to next(err) natively without requiring wrapper libraries.
Async Error Handling Pattern in Express 4
// Express 4 requires try-catch or explicit wrappers
app.get('/users/:id', async (req, res, next) => {
try {
const user = await User.findById(req.params.id);
if (!user) return res.status(404).send('Not Found');
res.json(user);
} catch (error) {
next(error); // Manual pass to global error handler
}
});💡 Express 4 requires explicit try-catch wrapping or async handler utility wrappers like express-async-errors.
Key Takeaways
- Express 4 requires manually catching async exceptions and invoking
next(err). - Express 5 automatically catches rejected promises in async route handlers.