acf-rich-editor-textarea-height.php

<?php

/*
 * -----------------------------------------------------------------------------
 * Advanced Custom Fields Modifications
 * -----------------------------------------------------------------------------
*/
// Only the style is working, the script is not, it might introduce bugs, but it less likely as the scroll is always active in the textarea.
function PREFIX_apply_acf_modifications() {
?>
  <style>
    .acf-editor-wrap textarea {
      max-height: 150px;
    }
  </style>
  <script>
    (function($) {
      // (filter called before the tinyMCE instance is created)
      acf.add_filter('wysiwyg_tinymce_settings', function(mceInit, id, $field) {
        // enable autoresizing of the WYSIWYG editor
        mceInit.wp_autoresize_on = true;
        return mceInit;
      });
      // (action called when a WYSIWYG tinymce element has been initialized)
      acf.add_action('wysiwyg_tinymce_init', function(ed, id, mceInit, $field) {
        // reduce tinymce's min-height settings
        ed.settings.autoresize_min_height = 50;
        // reduce iframe's 'height' style to match tinymce settings
        $('.acf-editor-wrap textarea').css('height', '150px');
      });
    })(jQuery)
  </script>
<?php
}

/*
 * -----------------------------------------------------------------------------
 * WordPress hooks
 * -----------------------------------------------------------------------------
*/
add_action('acf/input/admin_footer', 'PREFIX_apply_acf_modifications');