generate fields in Drupal 8

gistfile1.php

function generate_fields() {
  $field_name = 'field_gen_';
  $field_type = 'text';
  $field_formatter = 'text_default';
  $number = 100;

  for ($i = 1; $i <= $number; ++$i) {
    echo("creating field $i \n");
    entity_create('field_entity', array(
      'name' => $field_name . $i,
      'entity_type' => 'node',
      'type' => $field_type,
    ))->save();
    entity_create('field_instance', array(
      'entity_type' => 'node',
      'field_name' => $field_name . $i,
      'bundle' => 'article',
    ))->save();
    entity_get_display('node', 'article', 'default')
      ->setComponent($field_name . $i, array('type' => $field_formatter))
      ->save();
  }
}