[seletz]

We use ExtJS a lot. But I think the exact opposite is the case. With ExtJS, you have the usual double-binding, e.g. if you set this property of that Model somewhere in your view hierarchy some little snippet of HTML are inserted/removed from the DOM. It's basically side effects only.

If I understood it correctly, one can think of react app/page as a pure function taking data and producing a DOM.

Reasoning and testing pure functions should be much easier than a set of components which partly rely on side effects.