1. Introduction

1.1 Goal of the Tutorial

This tutorial aims to provide a comprehensive understanding of how to handle errors and implement logging in GraphQL.

1.2 Learning Outcomes

By the end of this tutorial, you should be able to:
- Understand the concepts of error handling and logging in GraphQL.
- Implement error handling and logging mechanisms in your GraphQL application.

1.3 Prerequisites

This tutorial assumes basic knowledge of GraphQL and JavaScript.

2. Step-by-Step Guide

2.1 Error Handling

Errors in GraphQL are not thrown like in REST APIs. Instead, they are added to the errors array in the response.

Best Practice

The best practice is to create error classes for each type of error that can occur in the application. These classes can extend the default Error class, and you can add any additional fields if needed.

2.2 Logging

Logging is crucial for debugging and monitoring the GraphQL server. You can use any logging library that suits your needs. In this tutorial, we'll use winston due to its wide usage and flexibility.

Best Practice

Keep your logs structured and easy to understand. Make sure to log important parts of the system, especially where errors can occur.

3. Code Examples

3.1 Error Handling

// Creating a custom error class
class UserInputError extends Error {
  constructor(message) {
    super(message);
    this.name = 'UserInputError';
  }
}

// Use the custom error class
if (!user) {
  throw new UserInputError('User not found');
}

This code creates a custom UserInputError class and throws the error when the user is not found.

3.2 Logging

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

// Logging an error
logger.error('Error message');

This code sets up winston to log errors to error.log and all logs to combined.log. It logs an error message with the error level.

4. Summary

In this tutorial, you have learned about error handling and logging in GraphQL. You now know how to create custom error classes and use winston for logging.

5. Practice Exercises

1. Create two more custom error classes, AuthenticationError and PermissionError, and throw them in appropriate situations.
2. Set up winston to also log to the console in addition to the log files.
3. Enhance the logging setup to include timestamps in the logs.

Remember, practice is key to mastering any concept. Happy coding!

Additional Resources

• GraphQL Official Documentation
• Winston GitHub
• Error handling in GraphQL