react-hook-form/app/src/defaultValues.tsx

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

function DefaultValues() {
  const { register } = useForm<{
    test: string;
    test1: {
      firstName: string;
      lastName: string[];
      deep: {
        nest: string;
      };
    };
    checkbox: string[];
  }>({
    defaultValues: {
      test: 'test',
      checkbox: ['1', '2'],
      test1: {
        firstName: 'firstName',
        lastName: ['lastName0', 'lastName1'],
        deep: {
          nest: 'nest',
        },
      },
    },
  });
  const [show, setShow] = React.useState(true);

  return (
    <>
      {show ? (
        <form>
          <input {...register('test')} />
          <input {...register('test1.firstName')} />
          <input {...register('test1.deep.nest')} />
          <input {...register('test1.deep.nest')} />
          <input {...register('test1.lastName.0')} />
          <input {...register('test1.lastName.1')} />
          <input type="checkbox" value={'1'} {...register('checkbox')} />
          <input type="checkbox" value={'2'} {...register('checkbox')} />
        </form>
      ) : null}
      <button type={'button'} id={'toggle'} onClick={() => setShow(!show)}>
        toggle
      </button>
    </>
  );
}

export default DefaultValues;