How to I access an entity (e.g. node) field in Drupal8

This function access an entity field on a node in Drupal8. It works the following way,

Checks to see if node exists
Gets the current nodes NID
Loads the entity that is attached to the NID
Returns the field name of the NID

/**
 * @param $fieldName
 * @return array of Objects
 */
function _access_a_nodes_field($fieldName) {
  if(\Drupal::routeMatch()->getParameter('node')){
    $nid = \Drupal::routeMatch()->getParameter('node');
    $node = \Drupal\node\Entity\Node::load($nid->id());
    return $node->get($fieldName)->getValue();
  }
  return NULL;
}