Template on Select2

Actually, I don't think the option js_options is working at all. Just tried adding allowClear and placeholder properties and it is still rendering with the default options (data-options="{"allowClear":true,"width":"none","placeholder":"Select an item"}"). Can you check, please? Tks.

These options worked, thanks. But I'm still having troubles with the templating. I don't know much PHP, so I'm having trouble to understand how this parameter would work. Taking your code as example:

add_filter( 'rwmb_meta_boxes', 'your_prefix_select_demo' );
function your_prefix_select_demo( $meta_boxes ) {
	$meta_boxes[] = array(
		'title' => __( 'Select Field Demo', 'your-prefix' ),
		'fields' => array(
			array(
				'name'       => __( 'Select Advanced', 'your-prefix' ),
				'id'         => 'select_advanced',
				'type'       => 'select_advanced',
				'options'    => array(
					'value1' => __( 'Label1', 'your-prefix' ),
					'value2' => __( 'Label2', 'your-prefix' ),
				),
				'js_options' => [
					'placeholder' => 'Select whatever you want',
					'allowClear'  => false,
					'templateSelection'  => formatState,
				],
			),
		),
	);
	return $meta_boxes;
} 

Being the formatState originally a JS function how am I supposed to use it? Should I pass the function call as a String and have it on a .js file or should I convert it to a PHP function? If I convert it to PHP function, how would I be able to get the 'state' object that is passed on the select2 example?

Sorry for the trouble. thanks.