type OnInvalid = ({
  invalidFields: Object[], // Unordered list of invalid fields
  fields: Object, // The state of the fields
  form: ReactComponent // Reference to the Form component
}) => void

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 }) => {
        // ...
    }
​
    render() {
        return (
            <Form onInvalid={this.handleInvalidForm}>
                <Input name="username" required />
                <button type="submit">Submit</button>
            </Form>
        )
    }
}