Understanding React Hook Form

Oct 13, 2025 by wbrum.org 3 views

Introduction

React Hook Form is a popular library for managing forms in React applications. It provides a simple and efficient way to handle form data, validation, and submission. However, one common requirement when working with forms is to detect when a value has been modified. In this article, we will explore how to achieve this using React Hook Form.

Understanding React Hook Form

Before diving into the solution, let's quickly review how React Hook Form works. When you create a form using React Hook Form, you typically use the useForm hook to manage the form data. The useForm hook returns an object with several properties, including register, handleSubmit, and formState.

The formState object contains information about the form's state, including whether the form is dirty (i.e., has been modified) or has been submitted. However, by default, the formState object does not provide a way to detect when a specific value has been modified.

Detecting Value Modifications

To detect when a value has been modified, you can use the register function returned by the useForm hook. The register function takes a field name as an argument and returns an object with several properties, including onChange and value.

The onChange property is a callback function that is called whenever the value of the field changes. You can use this callback function to update a state variable that indicates whether the form has been modified.

Here's an example of how you can use the register function to detect when a value has been modified:

import { useForm } from 'react-hook-form';
function MyForm() {
const { register, formState } = useForm();
const [edited, setEdited] = useState(false);
const handleInputChange = (event) => {
setEdited(true);
};
return (
<form>
<input
type="text"
...register('name', { onChange handleInputChange )}
defaultValue="John Doe"
/>
{edited && <p>Form has been modified!</p>}
</form>
);
}

In this example, we use the register function to register the name field and pass the onChange callback function to it. When the value of the name field changes, the handleInputChange function is called, which updates the edited state variable to true.

Using the `watch` Function

Another way to detect when a value has been modified is to use the watch function returned by the useForm hook. The watch function takes a field name as an argument and returns the current value of the field.

You can use the watch function to create a state variable that indicates whether the form has been modified. Here's an example:

import { useForm } from 'react-hook-form';
function MyForm() {
const { register, watch } = useForm();
const [edited, setEdited] = useState(false);
const handleInputChange = (event) => {
setEdited(true);
};
const name = watch('name');
return (
<form>
<input
type="text"
...register('name', { onChange handleInputChange )}
defaultValue="John Doe"
/>
{edited && <p>Form has been modified!</p>}
</form>
);
}

In this example, we use the watch function to get the current value of the name field and store it in the name variable. We then use this variable to update the edited state variable when the value of the name field changes.

Conclusion

In this article, we explored how to detect when a value has been modified using React Hook Form. We discussed two approaches: using the register function to detect changes to a specific field, and using the watch function to get the current value of a field.

By using these approaches, you can create a form that updates a state variable when a value has been modified, allowing you to perform additional actions or update the form's state accordingly.

Example Use Cases

Here are some example use cases for detecting value modifications using React Hook Form:

Saving form data: When a user modifies a form, you can save the updated data to a database or API.
Validating form data: When a user modifies a form, you can re-validate the data to ensure it meets the required criteria.
Updating form state: When a user modifies a form, you can update the form's state to reflect the changes.

By using React Hook Form to detect value modifications, you can create a more dynamic and responsive form that adapts to user input.

Best Practices

Here are some best practices to keep in mind when using React Hook Form to detect value modifications:

Use the register function: When using the register function, make sure to pass the onChange callback function to it to detect changes to a specific field.
Use the watch function: When using the watch function, make sure to store the current value of the field in a variable to update the form's state accordingly.
Update the form's state: When a user modifies a form, make sure to update the form's state to reflect the changes.

Introduction

In our previous article, we explored how to detect when a value has been modified using React Hook Form. In this article, we will answer some frequently asked questions (FAQs) about using React Hook Form to detect value modifications.

Q: What is the difference between `register` and `watch` in React Hook Form?

A: The register function is used to register a field with React Hook Form, while the watch function is used to get the current value of a field. The register function returns an object with several properties, including onChange and value, which can be used to detect changes to a specific field. The watch function, on the other hand, returns the current value of a field, which can be used to update the form's state accordingly.

Q: How do I use the `register` function to detect changes to a specific field?

A: To use the register function to detect changes to a specific field, you need to pass the onChange callback function to it. The onChange callback function will be called whenever the value of the field changes. You can then use this callback function to update the form's state accordingly.

Q: How do I use the `watch` function to get the current value of a field?

A: To use the watch function to get the current value of a field, you need to pass the field name as an argument to it. The watch function will return the current value of the field, which you can then use to update the form's state accordingly.

Q: Can I use both `register` and `watch` functions together?

A: Yes, you can use both register and watch functions together. The register function can be used to detect changes to a specific field, while the watch function can be used to get the current value of the field.

Q: How do I handle multiple fields with the same name?

A: When you have multiple fields with the same name, you need to use the register function with a unique key for each field. For example, if you have two fields with the name name, you can use the register function like this: { register('name1', { onChange: handleInputChange }) } and { register('name2', { onChange: handleInputChange }) }.

Q: Can I use React Hook Form with other form libraries?

A: Yes, you can use React Hook Form with other form libraries. React Hook Form is designed to be flexible and can be used with other form libraries.

Q: How do I handle form submission with React Hook Form?

A: To handle form submission with React Hook Form, you need to use the handleSubmit function returned by the useForm hook. The handleSubmit function will be called when the form is submitted, and you can use it to update the form's state accordingly.

Q: Can I use React Hook Form with functional components?

A: Yes, you can use React Hook Form with functional components. React Hook Form is designed to work with functional components and can be used with them.

Q: How do I handle errors with React Hook Form?

A: To handle errors with React Hook Form, you need to use the errors object returned by the useForm hook. The errors object contains information about the form's errors, and you can use it to display error messages to the user.

Conclusion

In this article, we answered some frequently asked questions about using React Hook Form to detect value modifications. We covered topics such as the difference between register and watch functions, how to use the register function to detect changes to a specific field, and how to handle multiple fields with the same name.

By following the best practices and guidelines outlined in this article, you can create a form that is both dynamic and responsive to user input.

Example Use Cases

Here are some example use cases for using React Hook Form to detect value modifications:

Saving form data: When a user modifies a form, you can save the updated data to a database or API.
Validating form data: When a user modifies a form, you can re-validate the data to ensure it meets the required criteria.
Updating form state: When a user modifies a form, you can update the form's state to reflect the changes.

By using React Hook Form to detect value modifications, you can create a more dynamic and responsive form that adapts to user input.

Best Practices

Here are some best practices to keep in mind when using React Hook Form to detect value modifications:

Use the register function: When using the register function, make sure to pass the onChange callback function to it to detect changes to a specific field.
Use the watch function: When using the watch function, make sure to store the current value of the field in a variable to update the form's state accordingly.
Update the form's state: When a user modifies a form, make sure to update the form's state to reflect the changes.

By following these best practices, you can create a form that is both dynamic and responsive to user input.