HTML forms?  Win32?  Curses&#x2F;INT9?<p>Unidirectional data flow has been mainstream at least as often as nests of observers and component state.  Probably moreso, if you count the 20 years of computing where the only thing you could do was batch processing.<p>What React does do is bring unidirectional data flow into the modern SPA web era.  That&#x27;s an accomplishment <i>now</i>, but it&#x27;s important to put it in its proper place in history.  Most of the history of programming had unidirectional data flow, it has its share of flaws as interfaces get more complex and interactive, and it&#x27;s likely that at some point in the future people will move back towards multidirectional data flow.