express_custom_error_handling_middleware_with_four_arguments.ts

1import express, { Request, Response, NextFunction } from 'express';
2
3const app = express();
4const port = 3000;
5
6// Regular route that triggers an error
7app.get('/', (req: Request, res: Response, next: NextFunction) => {
8  const err = new Error('Something went wrong!');
9  next(err); // Pass error to the error handling middleware
10});
11
12/**
13 * Official Error Handling Middleware
14 * Note: Error-handling middleware always takes four arguments. 
15 * You must provide four arguments to identify it as an error-handling middleware function.
16 */
17app.use((err: any, req: Request, res: Response, next: NextFunction) => {
18  console.error(err.stack);
19  res.status(500).send({
20    error: 'Internal Server Error',
21    message: err.message
22  });
23});
24
25app.listen(port, () => {
26  console.log(`Example app listening at http://localhost:${port}`);
27});