import React from 'react'
import { Form } from 'react-advanced-form'
import { Input } from 'react-advanced-form-addons'
export default class Example extends React.Component {
handleInvalidForm = ({ invalidFields, fields, form }) => {
<Form onInvalid={this.handleInvalidForm}>
<Input name="username" required />
<button type="submit">Submit</button>