Add "Other" option to allow for custom radio input with CMB2

cmb2-fields.php

<?php

if ( file_exists( dirname( __FILE__ ) . '/cmb2/init.php' ) ) {
  require_once dirname( __FILE__ ) . '/cmb2/init.php';
} elseif ( file_exists( dirname( __FILE__ ) . '/CMB2/init.php' ) ) {
  require_once dirname( __FILE__ ) . '/CMB2/init.php';
}

add_action( 'cmb2_admin_init', 'yourprefix_register_demo_metabox' );
/**
 * Hook in and add a demo metabox. Can only happen on the 'cmb2_admin_init' or 'cmb2_init' hook.
 */
function yourprefix_register_demo_metabox() {

  // Start with an underscore to hide fields from custom fields list
  $prefix = '_yourprefix_demo_';

  /**
   * Sample metabox to demonstrate each field type included
   */
  $cmb_demo = new_cmb2_box( array(
    'id'            => $prefix . 'metabox',
    'title'         => __( 'Test Metabox', 'cmb2' ),
    'object_types'  => array( 'page', ), // Post type
    // 'show_on_cb' => 'yourprefix_show_if_front_page', // function should return a bool value
    // 'context'    => 'normal',
    // 'priority'   => 'high',
    // 'show_names' => true, // Show field names on the left
    // 'cmb_styles' => false, // false to disable the CMB stylesheet
    // 'closed'     => true, // true to keep the metabox closed by default
  ) );

  $cmb_demo->add_field( array(
    'name'    => __( 'Test Radio With Custom Input', 'cmb2' ),
    'desc'    => __( 'field description (optional)', 'cmb2' ),
    'id'      => $prefix . 'radio',
    'type'    => 'radio_other',
    'show_option_none' => 'None',
    'show_option_other' => 'Custom Radio',
    'options' => array(
      'option1' => __( 'Option One', 'cmb2' ),
      'option2' => __( 'Option Two', 'cmb2' ),
      'option3' => __( 'Option Three', 'cmb2' ),
    ),
  ) );
}

cmb2_other_radio_option.php

<?php

add_action( 'cmb2_render_radio_other', 'yourprefix_radio_other', 10, 5 );
function radio_other( $field, $escaped_value, $object_id, $object_type, $field_type_object ) {
  $other = '';
  if ( $field->args && array_key_exists( 'show_option_other', (array) $field->args ) ) {

    $a = $field_type_object->parse_args( $args, 'list_input_other', array(
      'type'  => 'radio',
      'class' => 'cmb2-option',
      'name'  => $field_type_object->_name(),
      'id'    => $field_type_object->_id( 'other' ),
      'value' => '',
      'label' => $field->args['show_option_other'],
      'onclick' => sprintf( "document.getElementById('%s').focus()", $field_type_object->_id( 'othertext' ) ),
    ) );

    $b = $field_type_object->parse_args( $args, 'list_input_other_text', array(
      'type'  => 'text',
      'class' => 'cmb2-option',
      'name'  => '',
      'id'    => $field_type_object->_id( 'othertext' ),
      'value' => '',
      'label' => $field->args['show_option_other'],
      'onclick' => sprintf( "document.getElementById('%s').checked = true", $field_type_object->_id( 'other' ) ),
      'onkeyup' => sprintf( "document.getElementById('%s').value = document.getElementById('%s').value", $field_type_object->_id( 'other' ), $field_type_object->_id( 'othertext' ) ),
    ) );

    $input = sprintf( '<input%s/>', $field_type_object->concat_attrs( $b, array( 'label' ) ) );

    $other = sprintf( "\t" . '<li><input%s/> <label for="%s">%s</label> %s</li>' . "\n", $field_type_object->concat_attrs( $a, array( 'label' ) ), $a['id'], $a['label'], $input );
  }

  $a = $field_type_object->parse_args( $field, 'radio', array(
    'class'   => 'cmb2-radio-list cmb2-list',
    'options' => $field_type_object->concat_items( array( 'label' => 'test', 'method' => 'list_input' ) ),
    'desc'    => $field_type_object->_desc( true ),
  ) );

  printf( '<ul class="%s">%s%s</ul>%s', $a['class'], $a['options'], $other, $a['desc'] );
}

add_filter( 'cmb2_list_input_other_text_attributes', 'yourprefix_other_text_attributes', 10, 4 );
function other_text_attributes( $args, $defaults, $field, $field_type_object ) {
  $value = $field->escaped_value()
    ? $field->escaped_value()
    : $field->args( 'default' );

  if ( $value && ! array_key_exists( $value, $field->options() ) ) {
    $args['value'] = $value;
  }

  return $args;
}

add_filter( 'cmb2_list_input_other_attributes', 'yourprefix_other_radio_attributes', 10, 4 );
function other_radio_attributes( $args, $defaults, $field, $field_type_object ) {
  $value = $field->escaped_value()
    ? $field->escaped_value()
    : $field->args( 'default' );

  if ( $value && ! array_key_exists( $value, $field->options() ) ) {
    $args['checked'] = true;
    $args['value'] = $value;
  }

  return $args;
}