Nanobar
Very lightweight progress bars. No jQuery
Head js
The only script in your HEAD. Head JS loads JavaScript files in parallel like images without blocking the page. Your page will be faster. Even with a single combined file.
Lazysizes
High performance and SEO friendly lazy loader for images (responsive and normal), iframes and more, that detects any visibility changes triggered through user interaction, CSS or JavaScript without configuration.
Layzr.js
A small, fast, modern, and dependency-free library for lazy loading.
LABjs
Loading And Blocking JavaScript: On-demand parallel loader for JavaScript with execution order dependencies
Script.js
Asyncronous JavaScript loader and dependency manager