Add #ajax callback to an entity_autocomplete field
You can adjust the behavior with

'#ajax' =&gt; array(
  'event' =&gt; 'change',


This can be any javascript event. The default for a select is on 'change', for a normal field this is on 'blur'. But you can try any other event.

Reference: https://developer.mozilla.org/en-US/docs/Web/Events