remix-syntax/app/routes/contact.tsx

import { Form, useActionData, useTransition } from "remix";
import { sendEmail } from "~/utils/mailer";

export async function action({ request }) {
  let body = await request.formData();
  let name = body.get('name');
  let email = body.get('email');
  let message = await sendEmail({ to: email, text: name });
  return message;
}

export default function () {
  const data = useActionData();
  // Understand the page transition, and loading states and action states
  // If server side code is active, transition will tell you
  const transition = useTransition();

  return (
    <div>
      {data + " - " + transition.state}
      <h1>Contact Us</h1>
      {data === 'success' ? (
        <p>Your message has been sent!</p>
      ) : (
        <Form method="post">
          <label>
            Name:
          <input type="text" name="name" />
          </label>
          <label>
            Email:
            <input type="email" name="email" />
          </label>
          {transition.state === 'submitting' ? <p>Submitting...</p> : (<input type="submit" value="Send Message" />)}
        </Form>
      )}
    </div>
  )
}