Possible Answers to Your Question:
DevKit is intended as a development tool for customization– code should not really be kept there, but should be moved into a child theme. In the case of JS, you would put js snippets that augment a script that is already running. The customizer can’t do that without loading everything last, which may not be ideal for this script.
Try creating a child theme and then enqueuing the script properly using wp_enqueue_scripts as described here: