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MVVM: model change listeners on each state mutation: response to state mutation is immediate, never batch multiple listeners, requires dependency tracking (if the collection changed, then the count also changed). change listeners fire immediately and can trigger more change listeners. Lots of callbacks to keep track of and easy for things to get out of whack. (Backbone, Knockout, Knockback)
Angular ("MV-whatever"): state changes detected by dirty checking, but changes are immediate (digest loop), never needs dependency tracking. Digest loop runs until the state settles (no more change listeners fire) to ensure consistent views. Magic data binding.
Facebook React: state w/ dirty checking: state changes are always batched, views are a pure function, reconciliation step to merge desired view with existing view, no events or change listeners. Render process is a lot like a 3D game - draw the buffer, whack the buffer, loop. No magic. Facebook doesn't call it MVC but in my eyes it is.
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The more complex your view and state, the more events/mutations/callbacks, the more you need React.