Plugin Laser Loader is very small (4,9 KiB) and fast. The plugin adds a little loading progress bar at the top of the page to indicate that the next page is loading. You could see a similar UI pattern on YouTube or Medium.
Demo: https://codecanyon.net/item/laser-loader-stylish-progress-bar-preloader/26005913
source http://www.codelist.cc/plugins/241568-laser-loader-v102-stylish-progress-bar-preloader.html