Custom Error Types in TypeScript

Custom error types in TypeScript allow developers to create specific error classes tailored to their application's needs. These custom errors enhance error handling, improve code readability, and provide more detailed information about exceptional situations.

Creating Custom Error Types

To create a custom error type in TypeScript, you can extend the built-in Error class. This approach allows you to add custom properties and methods to your error objects.

class CustomError extends Error {
    constructor(message: string) {
        super(message);
        this.name = "CustomError";
    }
}
    

Using Custom Error Types

Once defined, custom error types can be thrown and caught like standard errors. They provide more context and allow for more specific error handling in your code.

function riskyOperation(value: number): void {
    if (value < 0) {
        throw new CustomError("Value cannot be negative");
    }
    // Proceed with operation
}

try {
    riskyOperation(-5);
} catch (error) {
    if (error instanceof CustomError) {
        console.log("Caught CustomError:", error.message);
    } else {
        console.log("Unexpected error:", error);
    }
}
    

Benefits of Custom Error Types

• Improved error categorization
• Enhanced debugging capabilities
• More precise error handling
• Better integration with TypeScript's type system

Best Practices

When working with custom error types in TypeScript, consider the following best practices:

1. Keep error names descriptive and specific
2. Include relevant error details in the constructor
3. Use type guards to narrow down error types in catch blocks
4. Consider creating an error hierarchy for complex applications

Integration with Promises

Custom error types work seamlessly with Promises in TypeScript, allowing for more granular error handling in asynchronous operations.

async function fetchData(url: string): Promise {
    try {
        const response = await fetch(url);
        if (!response.ok) {
            throw new CustomError(`HTTP error! status: ${response.status}`);
        }
        return await response.json();
    } catch (error) {
        if (error instanceof CustomError) {
            console.error("Custom fetch error:", error.message);
        } else {
            console.error("Unexpected error during fetch:", error);
        }
        throw error;
    }
}
    

By leveraging custom error types, TypeScript developers can create more robust and maintainable error handling systems, leading to improved application reliability and easier debugging processes.