Also what is the analogue to reactive in the past ? The main reason for reactive is different screen sizes and orientation of handheld devices. What similar problem would reactive have solved 2 decades ago ? There are a couple of references from 2001 and 2004 https://en.m.wikipedia.org/wiki/Responsive_web_design , but really there wasn't a practical common use case before the iPhone in 2007 and ipad in 2010.