Code snippet that can be used to redirect drupal 8 search form to custom result page.
<?php
/**
* @param $form
* @param \Drupal\Core\Form\FormStateInterface $form_state
* @param $form_id
*/
function mymodule_form_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id)
{
if ($form_id == 'search_block_form') {
$form['#action'] = '/mypage';
}
}
