Check if configuration with given name exists (like "has()") in active configuration.

drupal-active-config-key-exists.php

<?php

/**
 * Helper function / example code to check
 * if the given configuration (by name)
 * exists in active configuration.
 * @param string $configName
 *   The id of the configuration to check.
 *
 * @return boolean
 *
 /*
function isInActiveConfig($configId = 'core.extension'){
  $activeConfigFactory = \Drupal::service('config.factory');
  // The config factory always returns an ImmutableConfig object
  // but if doesn't exist in configuration yet, ->isNew() is true.
  $existsInActiveConfig = !$activeConfigFactory->get($configId)->isNew();
  return $existsInActiveConfig; 
}

?>

I was looking for something like $activeConfigFactory->has() but that doesn't exist. Here's the workaround to check the existence.