Try It Yourself - SyntaxStudy Editor

HTML / CSS / JS

// middleware/errors.js
class AppError extends Error {
    constructor(message, status = 500, code = 'INTERNAL_ERROR') {
        super(message);
        this.status = status;
        this.code   = code;
        this.isOperational = true;
    }
}

// Wrap async route handlers to forward rejections
function asyncHandler(fn) {
    return (req, res, next) => Promise.resolve(fn(req, res, next)).catch(next);
}

// Central error-handling middleware (register LAST)
function errorHandler(err, req, res, next) {
    const status = err.status || 500;
    const isProd = process.env.NODE_ENV === 'production';

// Always log the full error
    console.error(`[${req.method} ${req.path}]`, err);

res.status(status).json({
        error: {
            message: isProd && status === 500 ? 'Internal server error' : err.message,
            code:    err.code || 'INTERNAL_ERROR',
            ...(isProd ? {} : { stack: err.stack }),
        },
    });
}

// Usage in a route
const express = require('express');
const app     = express();
app.use(express.json());

app.get('/users/:id', asyncHandler(async (req, res) => {
    if (req.params.id === '0') throw new AppError('User not found', 404, 'NOT_FOUND');
    res.json({ id: req.params.id });
}));

app.use(errorHandler); // must be last
app.listen(3000);

module.exports = { AppError, asyncHandler, errorHandler };