Custom Error Types in TypeScript: A Guide to Better Error Handling

Error handling is a crucial part of any programming language, and TypeScript is no exception. One of the key features of TypeScript is its ability to create custom error types, which can help developers handle exceptions more effectively and in a way that fits their application's needs. In this article, we'll explore how to create custom error types in TypeScript, understand when and why to use them, and demonstrate best practices for error handling.

What are Custom Error Types in TypeScript?

In JavaScript, errors are usually handled using the built-in Error object. However, while this works in many cases, sometimes you need more specific error types to represent various issues within your application. TypeScript allows developers to create custom error types by extending the base Error class. This way, you can add additional properties and methods to your error objects, making it easier to track, debug, and handle different error scenarios in your code.

Why Use Custom Error Types?

1. 
   

   Better Readability: When you throw an error, it’s much more descriptive if you use a custom error type that clearly states the problem. For example, instead of a generic error, a custom error could say ValidationError or DatabaseConnectionError.

   
   


2. 
   

   Custom Properties: With a custom error type, you can include additional properties that may be useful for debugging, such as error codes, timestamps, or specific details about the error.

   
   


3. 
   

   Easier Debugging: Custom error types can make your code easier to maintain and debug. They provide more meaningful context about what went wrong and where, which speeds up troubleshooting.

   
   


4. 
   

   Catch Specific Errors: With custom error types, you can catch specific types of errors and handle them accordingly. This allows for more granular control over error handling and makes your code more robust.

   
   

How to Create a Custom Error Type in TypeScript

Creating a custom error type in TypeScript is simple. Here's a step-by-step guide:

1. 
   

   Create a new class that extends the Error class: To define a custom error type, you'll need to create a new class that extends the built-in Error class. This allows you to inherit all the properties and methods of the Error object while adding your own custom features.

   
   


2. 
   

   Set the error message and name: You can set a custom error message and specify a unique name for your error type to make it easy to identify later.

   
   


3. 
   

   Add custom properties (if necessary): If you need additional information about the error, you can add custom properties to your error class.

   
   

Example: Custom Error Type in TypeScript

In this example, we've created a ValidationError class that extends the Error class. The custom error includes a statusCode and details property, providing more information about the error. When we throw the error, we can catch it and check if it's an instance of the ValidationError class.

Best Practices for Working with Custom Errors

1. 
   

   Define Clear Error Types: Make sure your custom error types are descriptive and clearly indicate what kind of problem they represent. For example, instead of using a generic AppError, create more specific error types like NetworkError or DatabaseError.

   
   


2. 
   

   Use Custom Error Types for Specific Scenarios: Not every error needs to be a custom error type. Use custom errors for scenarios where it’s helpful to have more detailed information or specific handling logic.

   
   


3. 
   

   Handle Errors Gracefully: When catching custom errors, make sure to handle them properly. Logging, notifying the user, and retrying the operation are all potential strategies depending on the error type.

   
   


4. 
   

   Error Hierarchy: You can also create a hierarchy of error types. For example, you could have a base AppError class that is extended by other error types like ValidationError and DatabaseError. This allows you to catch all errors that extend AppError and handle them in a generic way.

   
   


5. 
   

   Document Error Types: Since custom error types add complexity to your application, it's important to document them clearly so other developers understand when and how to use them https://billwatch.net/news/custom-error-types-in-typescript/.

   
   

Conclusion

Custom error types in TypeScript provide a powerful way to improve error handling in your applications. By extending the base Error class, you can create more descriptive, manageable, and debug-friendly errors that enhance your code's maintainability and clarity. Implementing custom error types when appropriate can save time and effort, especially in large applications where generic errors may not be sufficient to address the complexities of the system.

Whether you're building a simple app or a large-scale project, leveraging custom error types will help you build a more robust and predictable error-handling strategy, improving both the user experience and the development process.