jQuery and jQuery-ujs are not required within app/assets/javascript/application.js and have been moved under/client and are managed by npm. The modules are exposed via entry point by client/webpack.client.base.config.js and, for jquery-ujs, in the client/webpack.client.rails.build.config.js and the client/webpack.client.rails.hot.config.js.
In application_non_webpack.js, it's critical that any libraries that depend on jQuery come after the inclusion
of the Webpack bundle.
Please refer to Considerations for jQuery with Rails and Webpack for further info.