http://swannodette.github.io/2013/12/17/the-future-of-javascript-mvcs/

In which David Nolen shows how |UIs built with persistent data
structures outperform those using mutable state, simply because you
can check for changes with a simple reference equality check. And you
get undo for free, and snapshots are trivial. And, because decent
persistent data structures share structure, it's memory efficient.

frank