vanilla-lazyload
LazyLoad is a lightweight (2.4 kB) and flexible script that speeds up your web application by deferring the loading of your below-the-fold images, videos and iframes to when they will enter the viewport. It's written in plain "vanilla" JavaScript, it leve
sitespeed.io
sitespeed.io is an open-source tool for comprehensive web performance analysis, enabling you to test, monitor, and optimize your website’s speed using real browsers in various environments.