form.jsx

<form
  onSubmit={handleSubmit(values => (
  new Promise((resolve, reject) => {
    // errorsForm returns an Object where keys are fields with errors and values are messages to show in form.
    const errors = this.errorsForm(values); 

    if (! isEmpty(errors)) {
      return reject(errors);
    }

    return postToMyServer(values)
      .then(() => {
        return resolve();
      });
  }))}
>