React Hook Form and persistent data on page reload

If persisting in the localStorage works you, here is how I achieved it.

Define a custom hook to for persisting the data

export const usePersistForm = ({
  value,
  localStorageKey,
}) => {
  useEffect(() => {
    localStorage.setItem(localStorageKey, JSON.stringify(value));
  }, [value, localStorageKey]);

  return;
};

Just use it in the form component

const FORM_DATA_KEY = "app_form_local_data";

export const AppForm = ({
  initialValues,
  handleFormSubmit,
}) => {
  // useCallback may not be needed, you can use a function
  // This was to improve performance since i was using modals
  const getSavedData = useCallback(() => {
    let data = localStorage.getItem(FORM_DATA_KEY);
    if (data) {
     // Parse it to a javaScript object
      try {
        data = JSON.parse(data);
      } catch (err) {
        console.log(err);
      }
      return data;
    }
    return initialValues;
  }, [initialValues]);

  const {
    handleSubmit,
    register,
    getValues,
    formState: { errors },
  } = useForm({ defaultValues: getSavedData() });
  const onSubmit: SubmitHandler = (data) => {
     // Clear from localStorage on submit
     // if this doesn’t work for you, you can use setTimeout
     // Better still you can clear on successful submission
    localStorage.removeItem(FORM_DATA_KEY);
    handleFormSubmit(data);
  };

  // getValues periodically retrieves the form data
  usePersistForm({ value: getValues(), localStorageKey: FORM_DATA_KEY });

  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      ...
    </form>
   )
}

I already faced this issue and implemented it by creating a custom Hook called useLocalStorage. But since you are using the React hook form, it makes the code a bit complicated and not much clean!

I suggest you simply use the light package react-hook-form-persist. The only work you need to do is to add useFormPersist hook after useForm hook. Done!

import { useForm } from "react-hook-form";
import useFormPersist from "react-hook-form-persist";

const yourComponent = () => {
  const {
    register,
    control,
    watch,
    setValue,
    handleSubmit,
    reset
  } = useForm({
    defaultValues: initialValues
  });

  useFormPersist("form-name", { watch, setValue });

  return (
    <TextField
      title='title'
      type="text"
      label='label'
      {...register("input-field-name")}
    />
    ...
  );
}

The state itself won't persist any data on page reload.
You need to add your state data to Local Storage.
Then load it back into the state on componentDidMount (useEffect with empty dependency array).

const Form = () => {
  const [formData, setFormData] = useState({})
  
  useEffect(() => {
    if(localStorage) {
      const formDataFromLocalStorage = localStorage.getItem('formData');
      if(formDataFromLocalStorage) {
        const formDataCopy = JSON.parse(formDataFromLocalStorage)
        setFormData({...formDataCopy})
      }
    }
  }, []);
  
  useEffect(() => {
    localStorage && localStorage.setItem("formData", JSON.stringify(formData))
  }, [formData]);
  
  const handleInputsChange = (e) => {
    setFormData({
      ...formData,
      [e.target.name]: e.target.value
    })
  }
  
  return (
    <div>
      <input 
        type="text" 
        name="firstName"
        placeholder='first name'
        onChange={e => handleInputsChange(e)}
        value={formData?.firstName}
      />
      <input 
        type="text" 
        name="lastName"
        placeholder='last name'
        onChange={e => handleInputsChange(e)}
        value={formData?.lastName}
      />
    </div>
  )
}