Resources
Grab this script and save it to the JS folder in your theme directory.
Installation
Add code to your child theme’s functions.php file or via a plugin that allows custom functions to be added, such as the Code snippets plugin. Avoid adding custom code directly to your parent theme’s functions.php file as this will be wiped entirely when you update the theme.
Remember to make sure the path matches your theme structure) to enqueue it.
https://gist.github.com/woogists/0ffaff39206992b0cd409132b0dbf727