Drupal 8 number field widget that uses commas to separate thousands

NumberCommasWidget.php

<?php

namespace Drupal\YourModule\Plugin\Field\FieldWidget;

use Drupal\Core\Field\FieldFilteredMarkup;
use Drupal\Core\Field\FieldItemListInterface;
use Drupal\Core\Field\WidgetBase;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Field\Plugin\Field\FieldWidget\NumberWidget;

/**
 * Plugin implementation of the 'number' widget.
 *
 * @FieldWidget(
 *   id = "number_with_commas",
 *   label = @Translation("Number with commas field"),
 *   field_types = {
 *     "integer",
 *     "decimal",
 *     "float"
 *   }
 * )
 */
class NumberCommasWidget extends NumberWidget {

  /**
   * {@inheritdoc}
   */
  public function formElement(FieldItemListInterface $items, $delta, array $element, array &$form, FormStateInterface $form_state) {
    $value = isset($items[$delta]->value) ? $items[$delta]->value : NULL;
    $field_settings = $this->getFieldSettings();

    // Use a textfield instead of a number field for this widget.
    // Preserve the number of decimal places, but add commas to numbers.
    $element += array(
      '#type' => 'textfield',
      '#default_value' => number_format($value, strlen(substr(strrchr($value, "."), 1)), '.', ','),
      '#placeholder' => $this->getSetting('placeholder'),
    );

    // Set minimum and maximum.
    if (is_numeric($field_settings['min'])) {
      $element['#min'] = $field_settings['min'];
    }
    if (is_numeric($field_settings['max'])) {
      $element['#max'] = $field_settings['max'];
    }

    // Add prefix and suffix.
    if ($field_settings['prefix']) {
      $prefixes = explode('|', $field_settings['prefix']);
      $element['#field_prefix'] = FieldFilteredMarkup::create(array_pop($prefixes));
    }
    if ($field_settings['suffix']) {
      $suffixes = explode('|', $field_settings['suffix']);
      $element['#field_suffix'] = FieldFilteredMarkup::create(array_pop($suffixes));
    }

    return array('value' => $element);
  }

  public function massageFormValues(array $values, array $form, FormStateInterface $form_state) {
    // Remove commas from numbers.
    foreach ($values as &$value) {
      $value = str_replace(',', '', $value);
    }
    return $values;
  }

}