Webpack
Packs CommonJs/AMD modules for the browser. Allows to split your codebase into multiple bundles, which can be loaded on demand. Support loaders to preprocess files, i.e. json, jade, coffee, css, less, ... and your custom stuff.
Query Loader2
Version of the QueryLoader by Gaya Design. Preload images with ease.
Script.js
Asyncronous JavaScript loader and dependency manager
LABjs
Loading And Blocking JavaScript: On-demand parallel loader for JavaScript with execution order dependencies
RequireJS
A file and module loader for JavaScript
Pilpil
Pilpil - Progressive Image Loading
jQuery Pjax
pushState + ajax = pjax
Oc Lazy Load
Load modules on demand (lazy load) in AngularJS
Queue
Yet another asynchronous helper library for JavaScript. 387 bytes minified and gzipped!
Blazy
bLazy is a lightweight lazy loading and multi-serving image script. It's written in JavaScript why it doesn't have any dependencies for 3rd party libraries like jQuery. bLazy is working in all modern browser including IE7+.
Nanobar
Very lightweight progress bars. No jQuery
Aload
Loads images, scripts, styles, iframes, videos and audio asynchronously.
Lazy Load Xt
Lazy load XT is a jQuery plugin for images, videos and other media
Sea.js
A Module Loader for the Web
Px Loader
PxLoader is a simple JavasScript library for creating preloaders and resource downloaders for HTML5 apps.
Layzr.js
A small, fast, modern, and dependency-free library for lazy loading.
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.