Because we want to update a specific item in the array without resorting to mutations, we have to slice it before and after the item. If you find yourself often writing such operations, it’s a good idea to use a helper like [react-addons-update](https://facebook.github.io/react/docs/update.html), [updeep](https://github.com/substantial/updeep), or even a library like [Immutable](http://facebook.github.io/immutable-js/) that has native support for deep updates. Just remember to never assign to anything inside the `state` unless you clone it first.