[fleabitdev]

The problem described by antris is that, if a developer were to naively tear down and rebuild the entire DOM tree on each state change, the browser would discard some important state which belongs to the old DOM nodes. This state includes the text selection, keyboard focus, mouse capture, scroll position, and the progress of CSS transitions and animations.

React solves this problem by building a virtual DOM, and then conservatively updating the actual DOM (sometimes just mutating individual HTML attributes!) so that this state is preserved.