Drupal 7, ajax on form, how to implement keyup event?

Question

Drupal

Good day!
In Drupal, by default, if you add #ajax to the form element without the event property, ajax fires after the element is unfocused (change). If I put:

'#type' => 'textfield',
'#ajax' => array(
    ...,
    'event' => 'keyup' // | keypress и тд
)

works, but after each entered character, the focus is reset from the field and therefore the input cannot be continued, you have to return the cursor back. Why is this happening? How to do it right?

Answer 1

Try like this:

'#type' => 'textfield',
'#ajax' => array(
    ...,
    'event' => 'keyup' // | keypress и тд
   'keypress' => TRUE,
)