Immer is a JavaScript library that lets you write state updates using normal mutable code, then automatically produces an immutable snapshot of the result. It's useful when you need immutable state (for change detection, undo/redo, or time-travel debugging) but find writing immutable operations tedious or error-prone. Under the hood, Immer uses copy-on-write to ensure only modified parts of your state are copied, keeping performance efficient.

mweststrate, aleclarson