React Hook Form – How to type the form data with TypeScript types?

This article provides information from Gemini AI regarding how to type React Hook Form form data.
The reasoning for this dialogue is due to there not being clear information about this, and the general loose typing that React Hook Form enforces.
The loose typing I talk about here is how using React Hook Form methods, types are made undefined or null even if the original type did not allow for this.
It seems that it is expected that fields may not be set, so handling of form data should take this into consideration, especially when submitting data.

Please see below for the AI dialogue with more details:

In react-hook-form, when submitting form data and using it for saving via an API, is it recommended to format the data?

It seems like it is easy to have an incorrect format of data due to how react-hook-form works.

Also, what type should I use for the useForm generic parameter to make sure the form data typing is loose enough to require proper checks and formatting?

Also should I trigger form submit with handleSubmit or trigger?

Formatting Form Data for API Submission with React Hook Form

Data Formatting: Absolutely Essential

Yes, it’s highly recommended to format your form data before sending it to the API.

React Hook Form provides a convenient way to manage form state, but it doesn’t inherently guarantee the data structure aligns perfectly with your API’s expectations. Common reasons for formatting include:

  • Data Type Conversion: Converting strings to numbers, dates, or other specific types.
  • Nested Data Structures: Transforming flat form data into nested objects or arrays.
  • API-Specific Formatting: Adhering to required formats like ISO 8601 dates, specific number formats, or custom data structures.
  • Data Validation: Implementing additional validation logic beyond what React Hook Form provides.

By formatting the data, you ensure data integrity and prevent potential API errors.

Generic Type for useForm

To maintain flexibility and accommodate potential data variations, consider using a generic type like any for the useForm parameter:

TypeScript
import { useForm } from 'react-hook-form';

const MyForm = () => {
  const { handleSubmit } = useForm<any>();

  const onSubmit = (data) => {
    // Format data here
    const formattedData = formatData(data);

    // Send formatted data to API
    api.post('/endpoint', formattedData);
  };

  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      {/* Your form elements */}
    </form>
  );
};

While any might seem less type-safe, it allows you to handle various data structures without strict type constraints. You can implement custom validation and formatting logic to ensure data correctness.

Triggering Form Submission

Use handleSubmit for form submission.

This is the recommended approach as it provides several benefits:

  • Handles form submission events: Automatically prevents default form behavior.
  • Provides access to form data: Passes the form data to the onSubmit handler.
  • Supports form state management: Manages form state (e.g., isSubmitting, isValid) for better user experience.
JavaScript
const { handleSubmit } = useForm();

const onSubmit = (data) => {
  // ...
};

return (
  <form onSubmit={handleSubmit(onSubmit)}>
    {/* Your form elements */}
  </form>
);

Avoid using trigger for form submission.

While trigger can be used to manually trigger validation, it’s not intended for submitting the form. Using handleSubmit is the standard and recommended way to handle form submissions.

Additional Considerations

  • Leverage TypeScript: If you’re using TypeScript, define custom types for your form data to improve type safety and code maintainability.
  • Create a separate formatting function: Extract data formatting logic into a reusable function for better code organization.
  • Consider a form library: Explore advanced form libraries like formik or yup for additional features and simplified data management.

By following these guidelines and carefully considering your specific requirements, you can effectively handle form data formatting and submission in React Hook Form.

Would you like to see a code example with data formatting and API submission?

any type seems a bit extreme. Is there another type I can use?

Refining the Generic Type in React Hook Form

You’re absolutely right. Using any as a generic type for useForm can be too permissive. Let’s explore more suitable options.

Understanding the Trade-off

The ideal type for useForm balances flexibility with type safety. We want to capture the general shape of the form data without being overly restrictive.

Potential Alternatives

  1. Interface or Type Alias:

    • Define an interface or type alias to outline the expected shape of your form data.
    • This provides basic structure and type checking.
    • Example:
    TypeScript
    interface FormData {
    name: string;
    email: string;
    age: number;
    // ... other properties
}

const { handleSubmit } = useForm<FormData>();

  2. Partial Type:

    • Use Partial<T> to make all properties of an interface optional.
    • This allows for flexibility in case some fields are not present.
    • Example:
    TypeScript
    interface FormData {
    name: string;
    email: string;
    age?: number; // Optional property
    // ... other properties
}

const { handleSubmit } = useForm<Partial<FormData>>();

  3. Generic Interface:

    • Create a generic interface with optional properties for maximum flexibility.
    • Example:
    TypeScript
    interface FormData<T extends Record<string, any>> {
    name: string;
    email: string;
    // ... other common properties
    additionalData?: T;
}

const { handleSubmit } = useForm<FormData<any>>();

Choosing the Right Approach

The best option depends on your specific use case:

  • If you have a well-defined form structure, a specific interface is suitable.
  • If you expect varying form data, a partial type or generic interface offers more flexibility.
  • Consider using TypeScript’s conditional types for more complex scenarios.

Additional Considerations

  • Leverage TypeScript’s Utility Types: Explore utility types like Record, Partial, and Omit to create tailored types.
  • Consider Validation Libraries: Integrate validation libraries like Yup or Zod for robust type checking and data transformation.
  • Balance Type Safety and Flexibility: Strive for a good balance between type safety and accommodating potential data variations.

By carefully considering these factors, you can select the appropriate generic type for your React Hook Form and enhance your application’s type safety.

Would you like to provide more details about your form structure so I can suggest a more specific type?

I’m specifically talking about using types provided by react-hook-form where I can use and pass my expected form data as a parameter to it.

Understanding and Utilizing React Hook Form Types

React Hook Form’s Built-in Types

Unfortunately, React Hook Form doesn’t provide a direct way to specify the entire form data structure as a generic type. The primary focus of its type definitions is on individual field-level interactions and validation.

Recommended Approach: Custom Interface or Type Alias

To achieve the desired level of type safety and structure for your form data, creating a custom interface or type alias is the most effective method. This aligns with the general practice of defining data structures in TypeScript.

Example:

TypeScript
interface MyFormData {
  name: string;
  email: string;
  address: {
    street: string;
    city: string;
    zipCode: string;
  };
  // ... other fields
}

const { handleSubmit } = useForm<MyFormData>();

Leveraging FieldValues for Flexibility

While not directly providing a structure, React Hook Form offers the FieldValues type which can be used as a base for your custom types. This provides some level of type safety and compatibility with the library.

Example:

TypeScript
import { FieldValues } from 'react-hook-form';

interface MyFormData extends FieldValues {
  // Additional properties specific to your form
  customField: string;
}

Key Points

  • Custom Types: Define clear and specific types for your form data.
  • FieldValues: Use FieldValues as a base for custom types if needed.
  • Type Safety: Prioritize type safety to catch potential errors early.
  • Flexibility: Consider using optional properties or generic types for dynamic form structures.

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