Page blocker Three types of page blocker DOM block CSSOM block Render block Demo npm install npm start References https://calendar.perfplanet.com/2012/deciphering-the-critical-rendering-path/ (TL;DR) https://developers.google.com/web/fundamentals/performance/critical-rendering-path/measure-crp https://www.w3.org/TR/html5/syntax.html#the-end