Error Handling Examples

This document provides practical examples of the improved error handling system.

Before and After Comparison
Common Use Cases
Error Response Examples
Validation Examples

Before and After Comparison

Example 1: Get By ID

Before:

async getById(req: Request, res: Response) {
  try {
    const id = Number(req.params.id);
    if (isNaN(id)) {
      return res.status(400).json({ error: 'Invalid ID' });
    }
    const item = await Service.getById(id);
    if (!item) {
      return res.status(404).json({ error: 'Not found' });
    }
    res.json(item);
  } catch (err) {
    console.error(err);
    res.status(500).json({ error: 'Internal error' });
  }
}

After:

async getById(req: Request, res: Response, next: NextFunction) {
  try {
    const id = validateId(req.params.id, 'id');
    const item = await Service.getById(id);
    if (!item) {
      throw new NotFoundError('Item', id);
    }
    res.json({ success: true, data: item });
  } catch (err) {
    next(err);
  }
}

Benefits:

✅ Cleaner code with less boilerplate
✅ Consistent error responses
✅ Better error messages
✅ Type-safe validation
✅ Centralized error handling

Example 2: Create Resource

Before:

async create(req: Request, res: Response) {
  try {
    const { name, email } = req.body;
    if (!name || !email) {
      return res.status(400).json({ error: 'Missing required fields' });
    }
    const item = await Service.create({ name, email });
    res.status(201).json(item);
  } catch (err) {
    console.error(err);
    if (err.message.includes('duplicate')) {
      res.status(409).json({ error: 'Already exists' });
    } else {
      res.status(500).json({ error: 'Failed to create' });
    }
  }
}

After:

async create(req: Request, res: Response, next: NextFunction) {
  try {
    validateRequiredFields(req.body, ['name', 'email']);
    
    const name = validateAndSanitizeString(req.body.name, 'name', {
      required: true,
      max: 255,
    });
    
    const email = validateAndSanitizeString(req.body.email, 'email', {
      required: true,
      max: 255,
    });
    
    validateEmail(email!, 'email');
    
    const item = await Service.create({ name: name!, email: email! });
    res.status(201).json({ success: true, data: item });
  } catch (err) {
    if (err instanceof ValidationError) {
      next(err);
    } else {
      next(new DatabaseError('Failed to create item', err as Error));
    }
  }
}

Benefits:

✅ Comprehensive validation
✅ Input sanitization
✅ Detailed error messages
✅ Proper error classification
✅ Security improvements

Common Use Cases

1. Validating Route Parameters

// Using validation utility
async getById(req: Request, res: Response, next: NextFunction) {
  try {
    const id = validateId(req.params.id, 'id');
    // ... rest of logic
  } catch (err) {
    next(err);
  }
}

// Using middleware
router.get('/:id', validateIdParam('id'), controller.getById);

2. Validating Required Fields

async create(req: Request, res: Response, next: NextFunction) {
  try {
    // Validate all required fields at once
    validateRequiredFields(req.body, ['name', 'email', 'password']);
    
    // ... rest of logic
  } catch (err) {
    next(err);
  }
}

// Or using middleware
router.post('/', 
  validateRequiredBodyFields(['name', 'email', 'password']),
  controller.create
);

3. Validating and Sanitizing Strings

async create(req: Request, res: Response, next: NextFunction) {
  try {
    const name = validateAndSanitizeString(req.body.name, 'name', {
      required: true,
      min: 2,
      max: 100,
    });
    
    const description = validateAndSanitizeString(req.body.description, 'description', {
      required: false,
      max: 500,
    });
    
    // ... rest of logic
  } catch (err) {
    next(err);
  }
}

4. Validating JSON Configuration

async create(req: Request, res: Response, next: NextFunction) {
  try {
    const { config } = req.body;
    
    if (config) {
      const parsed = validateJSON(config, 'config');
      // Use parsed object
    }
    
    // ... rest of logic
  } catch (err) {
    next(err);
  }
}

5. Handling Not Found

async getById(req: Request, res: Response, next: NextFunction) {
  try {
    const id = validateId(req.params.id, 'id');
    const item = await Service.getById(id);
    
    if (!item) {
      throw new NotFoundError('Item', id);
    }
    
    res.json({ success: true, data: item });
  } catch (err) {
    next(err);
  }
}

6. Handling Database Errors

async create(req: Request, res: Response, next: NextFunction) {
  try {
    // ... validation
    
    const item = await Service.create(data);
    res.status(201).json({ success: true, data: item });
  } catch (err) {
    if (err instanceof ValidationError) {
      next(err);
    } else {
      next(new DatabaseError('Failed to create item', err as Error));
    }
  }
}

7. Handling External Service Errors

async getPullRequestDetails(req: Request, res: Response, next: NextFunction) {
  try {
    const id = validateId(req.params.id, 'id');
    const pr = await PRService.getById(id);
    
    if (!pr) {
      throw new NotFoundError('Pull Request', id);
    }
    
    const details = await GitHubService.getPRDetails(pr.repo, pr.number);
    res.json({ success: true, data: details });
  } catch (err) {
    if (err instanceof ValidationError || err instanceof NotFoundError) {
      next(err);
    } else {
      next(new ExternalServiceError('GitHub', 'Failed to fetch PR details', err as Error));
    }
  }
}

Error Response Examples

1. Validation Error

Request:

POST /api/todos
Content-Type: application/json

{
  "description": "Some description"
}

Response:

{
  "success": false,
  "error": {
    "message": "Missing or invalid required fields",
    "code": "VALIDATION_ERROR",
    "statusCode": 400,
    "details": [
      {
        "field": "title",
        "message": "title is required",
        "code": "REQUIRED_FIELD"
      }
    ],
    "timestamp": "2024-01-20T10:30:00.000Z",
    "path": "/api/todos",
    "method": "POST"
  }
}

2. Not Found Error

Request:

GET /api/todos/999

Response:

{
  "success": false,
  "error": {
    "message": "Todo with id '999' not found",
    "code": "NOT_FOUND",
    "statusCode": 404,
    "timestamp": "2024-01-20T10:30:00.000Z",
    "path": "/api/todos/999",
    "method": "GET"
  }
}

3. Invalid ID Error

Request:

GET /api/todos/invalid

Response:

{
  "success": false,
  "error": {
    "message": "Invalid id",
    "code": "VALIDATION_ERROR",
    "statusCode": 400,
    "details": [
      {
        "field": "id",
        "message": "id must be a positive integer",
        "code": "INVALID_ID",
        "value": "invalid"
      }
    ],
    "timestamp": "2024-01-20T10:30:00.000Z",
    "path": "/api/todos/invalid",
    "method": "GET"
  }
}

4. Conflict Error

Request:

POST /api/apps
Content-Type: application/json

{
  "name": "My App",
  "code": "existing-code"
}

Response:

{
  "success": false,
  "error": {
    "message": "App code must be unique",
    "code": "CONFLICT",
    "statusCode": 409,
    "timestamp": "2024-01-20T10:30:00.000Z",
    "path": "/api/apps",
    "method": "POST"
  }
}

5. Invalid JSON Error

Request:

POST /api/apps
Content-Type: application/json

{
  "name": "My App",
  "code": "my-app",
  "e2eTriggerConfiguration": "{ invalid json }"
}

Response:

{
  "success": false,
  "error": {
    "message": "Invalid JSON in e2eTriggerConfiguration",
    "code": "VALIDATION_ERROR",
    "statusCode": 400,
    "details": [
      {
        "field": "e2eTriggerConfiguration",
        "message": "e2eTriggerConfiguration must be valid JSON",
        "code": "INVALID_JSON",
        "value": "{ invalid json }"
      }
    ],
    "timestamp": "2024-01-20T10:30:00.000Z",
    "path": "/api/apps",
    "method": "POST"
  }
}

6. Success Response

Request:

GET /api/todos/1

Response:

{
  "success": true,
  "data": {
    "id": 1,
    "title": "Complete documentation",
    "description": "Write comprehensive docs",
    "link": "https://github.com/...",
    "dueDate": "2024-01-25T00:00:00.000Z",
    "isCompleted": false
  }
}

Validation Examples

String Validation

// Required string with max length
const name = validateAndSanitizeString(req.body.name, 'name', {
  required: true,
  max: 255,
});

// Optional string with min and max length
const description = validateAndSanitizeString(req.body.description, 'description', {
  required: false,
  min: 10,
  max: 1000,
});

Email Validation

const email = validateAndSanitizeString(req.body.email, 'email', {
  required: true,
  max: 255,
});

validateEmail(email!, 'email');

URL Validation

const url = validateAndSanitizeString(req.body.url, 'url', {
  required: false,
  max: 500,
});

if (url) {
  validateURL(url, 'url');
}

Date Validation

const dueDate = req.body.dueDate;

if (dueDate) {
  const parsedDate = validateDate(dueDate, 'dueDate');
  // Use parsedDate
}

Enum Validation

const status = validateEnum(
  req.body.status,
  ['pending', 'active', 'completed'],
  'status'
);

Array Validation

const tags = validateArray(req.body.tags, 'tags', {
  minLength: 1,
  maxLength: 10,
});

Tips and Best Practices

Always validate input early in the controller before any business logic
Use specific error classes for different scenarios
Provide detailed error information to help API consumers
Sanitize user input to prevent injection attacks
Use consistent response format across all endpoints
Log errors with context for debugging
Don't expose sensitive information in error messages
Use middleware for common validations to reduce boilerplate
Test error scenarios to ensure proper error handling
Document error responses in API documentation

Table of Contents​

Before and After Comparison​

Example 1: Get By ID​

Example 2: Create Resource​

Common Use Cases​

1. Validating Route Parameters​

2. Validating Required Fields​

3. Validating and Sanitizing Strings​

4. Validating JSON Configuration​

5. Handling Not Found​

6. Handling Database Errors​

7. Handling External Service Errors​

Error Response Examples​

1. Validation Error​

2. Not Found Error​

3. Invalid ID Error​

4. Conflict Error​

5. Invalid JSON Error​

6. Success Response​

Validation Examples​

String Validation​

Email Validation​

URL Validation​

Date Validation​

Enum Validation​

Array Validation​

Tips and Best Practices​

Table of Contents

Before and After Comparison

Example 1: Get By ID

Example 2: Create Resource

Common Use Cases

1. Validating Route Parameters

2. Validating Required Fields

3. Validating and Sanitizing Strings

4. Validating JSON Configuration

5. Handling Not Found

6. Handling Database Errors

7. Handling External Service Errors

Error Response Examples

1. Validation Error

2. Not Found Error

3. Invalid ID Error

4. Conflict Error

5. Invalid JSON Error

6. Success Response

Validation Examples

String Validation

Email Validation

URL Validation

Date Validation

Enum Validation

Array Validation

Tips and Best Practices