We built our own immutable object utilities that prevent mutating anything in the object graph. These immutable objects look and feel just like regular objects/arrays, so you can use functional map/reduce etc. The only thing you can do with them besides reading their properties, is to create a new version of the previous object with changes applied. We then use object identity to detect when things could not have possibly changed between render cycles. We prune off those paths that will not need to be updated, justifying the pruning based on dependent data's object identity remaining the same over time. Same object identity across two points in time necessarily implies that their deeply immutable data structures have not changed, therefore their generated output could not have possibly changed.

I've seen two libraries suggested on the React mailing list:

http://swannodette.github.io/mori/

https://github.com/hughfdjackson/immutable

The first one uses the same data structures from ClojureScript.

I'm curious about this as well.