useForm - FormState

formState: Object

This object contains information about the entire form state. It helps you to keep on track with the user's interaction with your form application.

Return

Name	Type	Description
`isDirty`	`boolean`	Set to `true` after the user modifies any of the inputs. Important: 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. Do not support custom object, Class or File 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`. Important: Make sure to provide defaultValues at the useForm, so hook form can have a single source of truth to compare each field's dirtiness. 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 runtime error.
`isSubmitting`	`boolean`	`true` if the form is currently being submitted. `false` otherwise.
`isLoading`	`boolean`	`true` if the form is currently loading async default values. Important: this prop is only applicable to async `defaultValues` 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.
`validatingFields`	`boolean`	Capture fields which are getting async validation.
`errors`	`object`	An object with field errors. There is also an ErrorMessage component to retrieve error message easily.

Rules

formState is wrapped with a Proxy to improve render performance and skip extra logic if specific state is not subscribed to. Therefore make sure you invoke or read it before a render in order to enable the state update.

formState is updated in batch. If you want to subscribe to formState via useEffect, make sure that you place the entire formState in the optional array.

useEffect(() => {
  if (formState.errors.firstName) {
    // do the your logic here
  }
}, [formState]); // ✅ 
// ❌ formState.errors will not trigger the useEffect

Pay attention to the logical operator when subscription to formState.

// ❌ formState.isValid is accessed conditionally, 
// so the Proxy does not subscribe to changes of that state
return <button disabled={!formState.isDirty || !formState.isValid} />;
  
// ✅ read all formState values to subscribe to changes
const { isDirty, isValid } = formState;
return <button disabled={!isDirty || !isValid} />;

Examples

CodeSandbox ^JS

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

export default function App() {
  const {
    register,
    handleSubmit,
    // Read the formState before render to subscribe the form state through the Proxy
    formState: { errors, isDirty, isSubmitting, touchedFields, submitCount },
  } = useForm();
  const onSubmit = (data) => console.log(data);

  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      <input {...register("test")} />
      <input type="submit" />
    </form>
  );
}

Video

The following video will explain in detail different form states.