Hierarchical select for native Advanced Custom Fields taxonomy fields

hierearchical-select-acf.php

/* 

Got a hierarchical taxonomy in Wordpress? Want to make users select a top-level term first, 
then one of its children, then maybe one of its children? Me too! 

1. Create a native ACF taxonomy field, with multiple values allowed.
2. Add the following JS and PHP snippets to your theme / plugin - replace all instances of the field key with your own.

*/


/* PHP */

function custom_acf_taxonomy_hierarchy( $args, $field, $post_id ){
    $args['parent'] = empty($_POST['parent']) ? 0 : $_POST['parent'];    
    return $args;
}
add_filter('acf/fields/taxonomy/query/key=field_5c7634ca3413f', 'custom_acf_taxonomy_hierarchy',10,3);

script.js

/* Javascript / jQuery */

acf.add_filter('select2_ajax_data', function( data, args, $input, field, instance ){

	var target_field_key = 'field_5c7634ca3413f'; //YOUR TARGET FIELD KEY HERE

	if(data.field_key == target_field_key){
		var field_selector = '[name="acf[' + target_field_key + '][]"]'; //the select field holding the values already chosen
		if($(field_selector).val() != '' && $(field_selector).val() != null){
			var collections = $(field_selector).val();
			parent_id = collections.pop(); //parent of available options will be set to the last term selected
		}
		else{
			parent_id = 0; //nothing chosen yet, offer only top-level terms
		}
		data.parent = parent_id;
	}
  
  return data;

});