jQuery Pjax
pushState + ajax = pjax
Almond
A minimal AMD API implementation for use after optimized builds
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