Welcome to the lesson on Best Practices for Error Handling in GraphQL. In this lesson, we will explore how to handle errors effectively in your GraphQL API using Apollo Server 4 and TypeScript. Proper error handling is crucial for building reliable and user-friendly applications.

In REST API, a single error usually results in the entire request failing with an HTTP error status. However, In GraphQL, partial success is possible because errors are isolated to specific fields.

GraphQL treats errors as part of the response format. If any field in a query fails, it includes an errors array in the response. Common error types include:

• User Input Errors
• Authentication Errors
• Validation Errors
• System Errors

Since Apollo Server 4 removed built-in error classes, we'll create our own error handling system:

Let's implement error handling using our custom error classes:

Here's how to validate inputs using our custom error handling:

Apollo Server 4 allows you to customize error formatting using the formatError option:

Here's a complete example putting it all together:

And here's how to make queries to the server:

In this updated lesson, you learned:

• How to create custom error classes in Apollo Server 4
• Best practices for error handling and validation
• How to use the formatError function to customize error responses
• Type-safe approaches to both server and client-side code
• Modern GraphQL patterns including proper variable usage

Remember that good error handling not only improves the developer experience but also helps build more reliable and maintainable applications. Keep practicing these patterns in your GraphQL APIs!