React-hook-form doesn't set isDirty to false when back to initial state

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06-10-2024

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React Hook Form's "isDirty" Bug: Why It's Not Resetting Properly and How to Fix It

The Problem:

React Hook Form (RHF) is a popular library for building forms in React. It offers a powerful set of hooks and features, including the isDirty flag which indicates if a form has been modified since its initial state. However, there's a known issue where isDirty doesn't always reset to false when a form is returned to its initial values. This can lead to unexpected behavior, especially when you need to trigger actions based on form modifications.

Scenario and Code Example:

Let's say we have a simple form with an input field:

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

function MyForm() {
  const { register, handleSubmit, formState: { isDirty } } = useForm();

  const onSubmit = (data) => {
    console.log('Form submitted:', data);
  };

  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      <input type="text" {...register('name')} />
      <button type="submit">Submit</button>
      <div>Form is dirty: {isDirty ? 'Yes' : 'No'}</div>
    </form>
  );
}

export default MyForm;

If you type something in the input field and then clear it, the isDirty flag will remain true even though the form is back to its original state. This is the issue we're trying to address.

Understanding the Issue:

The problem arises from RHF's internal mechanisms for tracking form changes. It uses a defaultValues object to represent the initial state of the form. When you modify a field, RHF marks the form as dirty by comparing the current values to the initial values.

The issue occurs when the defaultValues object is mutated after initialization. If you're changing the values of the defaultValues object directly, for example, by updating it with new data or using it for another purpose, RHF won't recognize the updated values as the initial state. This can lead to the isDirty flag remaining true even when the form is visually back to its original state.

Solution:

To fix this issue, you should avoid mutating the defaultValues object after initialization. Instead, you can use the following approaches:

1. Clone the defaultValues object:

   const { register, handleSubmit, formState: { isDirty }, reset } = useForm({
     defaultValues: { name: '' }, // Initial values
   });
   
   // ...
   
   const handleReset = () => {
     // Clone the defaultValues object
     const newDefaultValues = { ...defaultValues };
     reset(newDefaultValues); // Reset the form with the cloned object
   };
   

2. Use reset() with an updated defaultValues object:

   const { register, handleSubmit, formState: { isDirty }, reset } = useForm({
     defaultValues: { name: '' },
   });
   
   const handleReset = () => {
     // Update the defaultValues object with the new values
     const updatedDefaultValues = { name: 'John Doe' }; 
     reset(updatedDefaultValues);
   };
   

Additional Insights:

• Always use the reset() function from RHF to reset the form to its initial state.
• Be cautious about modifying the defaultValues object directly after initialization.
• If you need to dynamically change the initial values of the form, consider using a separate state variable to store the current default values and update them accordingly.

Conclusion:

The isDirty flag in React Hook Form is a valuable tool for tracking form changes. However, it's crucial to understand the way RHF manages form states to avoid unexpected behavior. By following the recommended approaches, you can ensure that isDirty is properly reset to false when the form returns to its initial state.