minimal-react-form.js

class MyForm extends React.Component {
  constructor() {
    super();
    this.handleSubmit = this.handleSubmit.bind(this);
  }

  handleSubmit(event) {
    event.preventDefault();
    const data = new FormData(event.target);
    
    fetch('/api/form-submit-url', {
      method: 'POST',
      body: data,
    });
  }

  render() {
    return (
      <form onSubmit={this.handleSubmit}>
        <label htmlFor="username">Enter username</label>
        <input id="username" name="username" type="text" />

        <label htmlFor="email">Enter your email</label>
        <input id="email" name="email" type="email" />

        <label htmlFor="birthdate">Enter your birth date</label>
        <input id="birthdate" name="birthdate" type="text" />

        <button>Send data!</button>
      </form>
    );
  }
}

Just a heads up, node's body-parser package doesn't support FormData being sent from the front-end.

I needed to JSON.stringify the body and pass a JSON header, like:

fetch('/api/add-user', {
      method: 'post',
      body: JSON.stringify({
        name: data.get('name'),
        email: data.get('email'),
        country: data.get('country')
      }),
      headers:{
        'Content-Type': 'application/json'
      }
    });