How do I handle errors in a TypeScript Express application?

How do I handle errors in a TypeScript Express application?

In a TypeScript Express application, you can handle errors by creating a custom error handling middleware. This middleware should be defined after all your routes. Here's a basic example:

import express, { Request, Response, NextFunction } from 'express';

const app = express();

// Your routes here

// Error handling middleware
app.use((err: Error, req: Request, res: Response, next: NextFunction) => {
    console.error(err.stack);
    res.status(500).send('Something broke!');
});

app.listen(3000, () => {
    console.log('Server is running on port 3000');
});

Can I create custom error classes for better error handling?

Yes, you can create custom error classes to handle different types of errors more effectively. Here's an example:

class AppError extends Error {
    public statusCode: number;
    public isOperational: boolean;

    constructor(message: string, statusCode: number, isOperational = true) {
        super(message);
        this.statusCode = statusCode;
        this.isOperational = isOperational;
        Error.captureStackTrace(this, this.constructor);
    }
}

// Usage in your error handling middleware
app.use((err: AppError, req: Request, res: Response, next: NextFunction) => {
    res.status(err.statusCode || 500).send(err.message);
});

How can I log errors to an external service?

You can use logging libraries like Winston or integrate with services like Sentry. For example, with Winston:

import winston from 'winston';

const logger = winston.createLogger({
    level: 'error',
    format: winston.format.json(),
    transports: [
        new winston.transports.File({ filename: 'error.log' })
    ],
});

app.use((err: Error, req: Request, res: Response, next: NextFunction) => {
    logger.error(err.message);
    res.status(500).send('Internal Server Error');
});