[vaylian]

There's a difference between document-based web sites like this one and web applications. The potential for web applications has mostly emerged as a side effect of the introduction of JavaScript. Back then, JavaScript was supposed to only add minor enhancements to web sites.

[ptx]

Well... Right here on the the very first website Tim Berners-Lee talks about how to build interactive web applications (here called "gateways"), albeit server-side rather than client-side: https://info.cern.ch/hypertext/WWW/FAQ/Server.html