MS have been doing declarative UIs for literally 8 years (XAML).
This is in contrast to a model where you mutate an existing UI model each time something interesting happens.
React is closer to an immediate-mode UI model: you write programs that compute exactly what the UI should look like on each frame, rather than mutating a scene graph each time something interesting happens (as occurs in retained-mode UI models). Substitute DOM for scene graph, and the distinction might hold.
But I'm not sure.
But yes, exactly. React is similar to an immediate mode graphics API. Except that also has weird connotations, because people think of things like canvas that are very low-level: all you get are lines, arcs, and fills. React's primitives are at the same level of abstraction as the DOM, you just work with them in immediate mode, not retained mode.
In contrast, a UI model like WPF uses (declarative) data binding to achieve something similar, but without as much flexibility and with more verbosity.
I'm working on a system that allows for state retention in an immediate mode model, though wrapping WPF rather than HTML:
http://research.microsoft.com/en-us/people/smcdirm/managedti...