How to check and change default front page programmatically in Drupal 8

To get current front page value:

$frontPage = \Drupal::configFactory()
  ->get('system.site')
  ->get('page.front');

To check if current page is the front page:

$isFront = \Drupal::service('path.matcher')->isFrontPage();

To change the front page to a new path:

\Drupal::configFactory()
  ->getEditable('system.site')
  ->set('page.front', '/dashboard')
  ->save();

More info:

• Configuration objects by default are immutable.