Why use a custom ApiError class with asyncHandler?
ApiError carries a status and message, so the error handler can return the right status code and a safe message. Combined with asyncHandler, async handlers read cleanly: throw new ApiError(404, 'User not found') and the rest is handled.
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More FAQs in Async Error Handling in Express: Best Practices
Wrap async handlers with asyncHandler: Promise.resolve(fn(req, res, next)).catch(next). The wrapper catches promise rejections and passes them to the error handler. Then you can throw inside async handlers.
Express 4 was designed before async/await. It does not catch promise rejections from async handlers. The handler returns a rejected promise that Express ignores, and the client hangs.
Yes. Express 5 catches promise rejections from async handlers and passes them to the error handler. The asyncHandler wrapper is still useful for older versions.
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