Immutable updates in JS have always required making copies of each level of nesting that has to be updated [0]. However, that process is very tedious and error

Immutable updates in JS have always required making copies of each level of nesting that has to be updated [0]. However, that process is very tedious and error-prone due to writing lots of nested spread operations. Immer effectively does those same steps, but automatically. This is all completely different than how Mobx works. Immer has a slight performance overhead [1], but in practice reducer logic is almost never a meaningful perf bottleneck in a React+Redux app - the cost of updating the UI is might higher. It's also worth noting that Immer was actually created by Michel Weststrate, the author of Mobx :) [0] https://redux-toolkit.js.org/usage/immer-reducers#basics-of-immutability https://redux-toolkit.js.org/usage/immer-reducers#basics-of-... [1] https://immerjs.github.io/immer/docs/performance https://immerjs.github.io/immer/docs/performance