Use Refs With Functional Components

You do not need to use class components for refs to work. You can do that with functional components by making use of closures in JS.

function CustomForm ({ handleSubmit }) {
  let inputElement;

  return (
    <form onSubmit={() => handleSubmit(inputElement.value)}>
      <input
        type='text'
        ref={(input) => inputElement = input} />
      <button type='submit'>Submit</button>
    </form>
  );
}