Import config programmatically in Drupal 8

index.php

<?php
use Drupal\Core\Config\ConfigImporter;
use Drupal\Core\Config\StorageComparer;
use Drupal\Core\Config\ConfigException;  

/**
 * Imports configurations programmaticaly in Drupal 8.
 *
 * Makes the same action as `drush cim -y`.
 * Based on the code from config.drush.inc:drush_config_import method.
 */
function configuration_import() {
  $storage_comparer = new StorageComparer(
    \Drupal::service('config.storage.sync'),
    \Drupal::service('config.storage'),
    \Drupal::service('config.manager')
  );

  $config_importer = new ConfigImporter(
    $storage_comparer,
    \Drupal::service('event_dispatcher'),
    \Drupal::service('config.manager'),
    \Drupal::lock(),
    \Drupal::service('config.typed'),
    \Drupal::moduleHandler(),
    \Drupal::service('module_installer'),
    \Drupal::service('theme_handler'),
    \Drupal::service('string_translation')
  );

  // Make sure configuration has changes.
  if ($storage_comparer->createChangelist()->hasChanges()) {
    // Import configurations.
    $config_importer->import();

    // There is an error during config import.
    if ($config_importer->getErrors()) {
      throw new ConfigException('Errors occurred during import');
    }
  }
}