useFormState: ({ control: Control }) => FormState

This custom hook allows you to subscribe to each form state, and isolate the re-render at the custom hook level. It has its scope in terms of form state subscription, so it would not affect other useFormState and useForm. Using this hook can reduce the re-render impact on large and complex form application.

Props

The following table contains information about the arguments for useFormState.

Name	Type	Description
`control`	`object`	`control` object provided by `useForm`. It's optional if you are using FormContext.
`name`	`string \| string[]`	Provide a single input name, an array of them, or subscribe to all inputs' formState update.
`disabled`	`boolean = false`	Option to disable the subscription.
`exact`	`boolean = false`	This prop will enable an exact match for input name subscriptions.

Return

Name	Type	Description
`isDirty`	`boolean`	Set to `true` after the user modifies any of the inputs. Make sure to provide all inputs' defaultValues at the useForm, so hook form can have a single source of truth to compare whether the form is dirty. `const { formState: { isDirty, dirtyFields }, setValue, } = useForm({ defaultValues: { test: "" } }); // isDirty: true setValue('test', 'change') // isDirty: false because there getValues() === defaultValues setValue('test', '')` File typed input will need to be managed at the app level due to the ability to cancel file selection and FileList object.
`dirtyFields`	`object`	An object with the user-modified fields. Make sure to provide all inputs' defaultValues via useForm, so the library can compare against the `defaultValues`. Dirty fields will not represent as `isDirty` formState, because dirty fields are marked field dirty at field level rather the entire form. If you want to determine the entire form state use `isDirty` instead.
`touchedFields`	`object`	An object containing all the inputs the user has interacted with.
`defaultValues`	`object`	The value which has been set at useForm's defaultValues or updated defaultValues via reset API.
`isSubmitted`	`boolean`	Set to `true` after the form is submitted. Will remain `true` until the `reset` method is invoked.
`isSubmitSuccessful`	`boolean`	Indicate the form was successfully submitted without any `Promise` rejection or `Error` been thrown within the `handleSubmit` callback.
`isSubmitting`	`boolean`	`true` if the form is currently being submitted. `false` otherwise.
`isLoading`	`boolean`	`true` if the form is currently loading async default values. `const { formState: { isLoading } } = useForm({ defaultValues: async () => await fetch('/api') });`
`submitCount`	`number`	Number of times the form was submitted.
`isValid`	`boolean`	Set to `true` if the form doesn't have any errors. `setError` has no effect on `isValid` formState, `isValid` will always derived via the entire form validation result.
`isValidating`	`boolean`	Set to `true` during validation.
`errors`	`object`	An object with field errors. There is also an ErrorMessage component to retrieve error message easily.

Rules

Returned formState is wrapped with Proxy to improve render performance and skip extra computation if specific state is not subscribed, so make sure you deconstruct or read it before render in order to enable the subscription.

const { isDirty } = useFormState(); // ✅
const formState = useFormState(); // ❌ should deconstruct the formState

Examples

CodeSandbox ^TS

import * as React from "react";
import { useForm, useFormState } from "react-hook-form";

export default function App() {
  const { register, handleSubmit, control } = useForm({
    defaultValues: {
      firstName: "firstName"
    }
  });
  const { dirtyFields } = useFormState({
    control
  });
  const onSubmit = (data) => console.log(data);

  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      <input {...register("firstName")} placeholder="First Name" />
      {dirtyFields.firstName && <p>Field is dirty.</p>}
      
      <input type="submit" />
    </form>
  );
}

Thank you for your support

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