React Advanced Form - Async validation

RegistrationForm.jsx

import React from 'react';
import { Form } from 'react-advanced-form';

export default class RegistrationForm extends React.Component {
  validateEmail = ({ value, fieldProps, fields, form }) => {
    return fetch('https://backend/', { body: value })
      .then(res => res.json())
      .then((res) => {
        return {
         /* Determine if the e-mail is valid based on response */
         valid: (res.statusCode === 'SUCCESS'),
         errorCode: res.errorCode
        };
    });
  }
  
  render() {
    return (
      <Form>
        <Input
          name="userEmail"
          type="email"
          asyncRule={this.validateEmail}
          required />
          
        { /* Rest fields */ }
      </Form>
    );
  }
}