Rails Asset Pipeline - Seperate JavaScript file loaded before CDN

Having trouble understanding the asset pipeline in rails. I have a seperate JS file that makes an ajax call to my rails route and manipulate the DOM. However right now I have my custom JS script above the closing < /body > tag in the main application.html.erb I tried to make a separate js file in the asset/js folder and I'm pretty sure my js file gets compiled before the CDN gets loaded. How can I get the CDN to load first then my separate js file to load last?

Thanks