How to change user field value after node form is submitted?
As @Clive says, form submit handler is a bit too late. Do it in hook_node_presave or hook_entity_presave. If you do it in hook_node_presave:


Check the node type first: if ($node-&gt;bundle() === 'article')
Get the current user:
$user = User::load(\Drupal::currentUser()-&gt;id());
Then set the field value: $value = (int) $user-&gt;get('field_reputation')-&gt;getString() + 10; $user-&gt;set('field_reputation', $value); (I'm not 100% sure on this code, but I'm sure there are better ways to do it when you have more than 5 minutes :D. Feels dirty to use getString() and then type-cast it into int)
Save the user entity with $user-&gt;save();


If you use hook_entity_presave then you just need to check for the entity type additionally: $entity-&gt;getEntityType-&gt;Id() === 'node'