 `ReferenceError: ajaxurl is not defined` in `/wp-content/plugins/chef-forms/js/forms-front.js?ver=4.7.4`

Rendered pages which load `/wp-content/plugins/chef-forms/js/forms-front.js?ver=4.7.4` (sorry I don't know the location of the source) suffers from the problem `ReferenceError: ajaxurl is not defined` described in:

- https://wordpress.stackexchange.com/questions/190297/ajaxurl-not-defined-on-front-end

A possible solution is decribed there as well.

