Say you want a form with as-you-type validation. You can't have a view containing the whole form and just re-render that as someone types. If you did, you'd lose the user current focus on every render. This forces you to manipulate parts of the DOM "by hand", something React abstracts for you.
I find Backbone events extremely hard to work with (error-prone, super hard to test / debug), because there are many operations that emit tons of events. So you either listen+render() on any event (very inconsistent performance if your app has any kind of complexity), or you hand-pick the events you want to react to (event-hell). Using immutable objects along with React's PureRenderMixin means you can just render() on any change, with great performance. It makes your UI purely functional, very easy to reason about, and easy to test.
> You can't have a view containing the whole form and just re-render that as someone types. If you did, you'd lose the user current focus on every render. This forces you to manipulate parts of the DOM "by hand", something React abstracts for you.
This is not how most modern view engines work. Somehow the React community has convinced the entire JS world that they invented the idea of "only render what has changed" when that's just not the case.
Reread that in the context of the parent's statement. There is a misconception that every other template library blows away parts of the dom on each update and that only React will do something like input.value=newValue, but this is not the case.
I sure don't see where that misconception is the fault of "the React community."
In fact, this comment is the first time I've seen that formulated. I'll be honest, I don't read every React-related forum entry on the Internet, so I may have missed someone somewhere spreading such a misconception, but there certainly is no such centrally communicated premise.
React only "renders" everything within its shadow DOM. It then applies the results of diffing the previous and current version trying to use the most atomic operation (innerText, add/removeClass, add/removeNode, etc)
I find Backbone events extremely hard to work with (error-prone, super hard to test / debug), because there are many operations that emit tons of events. So you either listen+render() on any event (very inconsistent performance if your app has any kind of complexity), or you hand-pick the events you want to react to (event-hell). Using immutable objects along with React's PureRenderMixin means you can just render() on any change, with great performance. It makes your UI purely functional, very easy to reason about, and easy to test.