React itself does not allocate a new object, but it forces you to do it yourself: to update the application state, you're supposed to call `setState()` with a brand new state (which is a newly allocated object). In React tutorial[1], you can notice the use of the `Object.assign` pattern which perform a new allocation.

However, most JS runtime have a generational GC so an allocation isn't remotely as costly as an allocation in C or Rust.

[1] https://reactjs.org/tutorial/tutorial.html#why-immutability-...

> React itself does not allocate a new object, but it forces you to do it yourself: to update the application state, you're supposed to call `setState()` with a brand new state (which is a newly allocated object)

Afaik you don't have to. It just makes things easier since state changes can be detected through shallow reference comparisons. There is even the shouldComponentUpdate() hook to allow the user to detect state changes which did not trigger a whole state object change.

Doesn't make sense. You don't provide an entirely new object when you call `setState()`, just the parts of it that have changed.

When you use `Object.assign()` then you're doing it, but you don't have to use that, and probably shouldn't.