react-hook-form/examples/V7/asyncSubmitValidation.tsx

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

const sleep = (ms) => new Promise((resolve) => setTimeout(resolve, ms));

export default function App() {
  const {
    register,
    handleSubmit,
    formState: { errors },
    setError,
  } = useForm();

  const onSubmit = async (data) => {
    await sleep(2000);
    if (data.username === 'bill') {
      alert(JSON.stringify(data));
    } else {
      alert('There is error');
      setError('username', 'validate');
    }
  };

  console.log(errors);

  return (
    <div className="App">
      <form onSubmit={handleSubmit(onSubmit)}>
        <div>
          <label htmlFor="username">User Name</label>
          <input id="username" placeholder="Bill" {...register('username')} />
        </div>

        <div>
          <label htmlFor="lastName">Last Name</label>
          <input id="lastName" placeholder="Luo" {...register('lastName')} />
        </div>

        <div>
          <label htmlFor="email">Email</label>
          <input
            id="email"
            placeholder="bluebill1049@hotmail.com"
            type="text"
            {...register('email')}
          />
        </div>

        <div style={{ color: 'red' }}>
          {Object.keys(errors).length > 0 &&
            'There are errors, check your console.'}
        </div>
        <button type="submit">Submit</button>
      </form>
    </div>
  );
}