drupal_js_defaults() is deprecated

drupal_js_defaults() was introduced to provide the default data array for JavaScript attachments when hook_js_alter() was first added to Drupal 7. In Drupal 8 the asset attachment subsystem has been overhauled and while hook_js_alter() still exists, adding JavaScript should now usually be done via libraries and the alter hook only used in exceptional circumstances.

The defaults function has been removed with no replacement.