Node.jsError handling middleware có 4 tham số (err, req, res, next) — phải đăng ký CUỐI CÙNG sau tất cả routes.
- Pattern tốt nhất: tạo custom AppError class
class AppError extends Error { constructor(public statusCode: number, message: string, public isOperational = true) { super(message) } }— phân biệt operational errors (404, validation fail — dự đoán được) vs programming errors (null reference — bugs). - Async error wrapper để tránh try/catch lặp lại:
const asyncHandler = (fn) => (req, res, next) => Promise.resolve(fn(req, res, next)).catch(next). - Centralized error handler kiểm tra
err.isOperational: nếu true thì gửi message cho client, nếu false thì log và trả 500 generic. - Express 5 async routes tự động forward error nên không cần wrapper nữa.
- Lưu ý: quên
nexttham số thứ 4 → Express không nhận ra là error handler. - Không gọi
next()saures.json()trong error handler → double response error.
Error handling middleware has 4 parameters (err, req, res, next) — it MUST be registered LAST, after all routes.
- Best pattern: create a custom AppError class
class AppError extends Error { constructor(public statusCode: number, message: string, public isOperational = true) { super(message) } }— distinguishes operational errors (404, validation fail — expected) from programming errors (null reference — bugs). - Async error wrapper to avoid repeated try/catch:
const asyncHandler = (fn) => (req, res, next) => Promise.resolve(fn(req, res, next)).catch(next). - The centralized error handler checks
err.isOperational: if true, send the message to the client; if false, log it and return a generic 500. - Express 5 automatically forwards async errors so no wrapper is needed.
Pitfall: forgetting the 4th next parameter means Express won't recognize it as an error handler.