express-error-handling

# Express Error Handling Skill

Patterns for comprehensive error handling in Express.js.

## Error Class Hierarchy

### Base Application Error

```typescript
export class AppError extends Error {
  public readonly statusCode: number
  public readonly code: string
  public readonly isOperational: boolean

  constructor(
    message: string,
    statusCode: number = 500,
    code: string = 'INTERNAL_ERROR',
    isOperational: boolean = true
  ) {
    super(message)
    this.statusCode = statusCode
    this.code = code
    this.isOperational = isOperational

    Error.captureStackTrace(this, this.constructor)
  }
}
```

### Specific Error Classes

```typescript
export class NotFoundError extends AppError {
  constructor(resource: string, id?: string) {
    const message = id
      ? `${resource} with ID ${id} not found`
      : `${resource} not found`
    super(message, 404, 'NOT_FOUND')
  }
}

export class ValidationError extends AppError {
  public readonly details: Record<string, string[]>

  constructor(message: string, details: Record<string, string[]> = {}) {
    super(message, 400, 'VALIDATION_ERROR')
    this.details = details
  }
}

export class UnauthorizedError extends AppError {
  constructor(message: string = 'Unauthorized') {
    super(message, 401, 'UNAUTHORIZED')
  }
}

export class ForbiddenError extends AppError {
  constructor(message: string = 'Forbidden') {
    super(message, 403, 'FORBIDDEN')
  }
}

export class ConflictError extends AppError {
  constructor(message: string) {
    super(message, 409, 'CONFLICT')
  }
}

export class RateLimitError extends AppError {
  public readonly retryAfter: number

  constructor(retryAfter: number = 60) {
    super('Too many requests', 429, 'RATE_LIMIT_EXCEEDED')
    this.retryAfter = retryAfter
  }
}
```

## Error Handler Middleware

### Main Error Handler

```typescript
import { Request, Response, NextFunction } from 'express'

interface ErrorResponse {
  error: {
    code: string
    message: string
    det