Winner of the "Breakthrough of the year" [React open source award](https://osawards.com/react/) and "Most impactful contribution" [JavaScript open source award](https://osawards.com/javascript/) in 2019.
- Introduction blogpost: [Immer: Immutability the easy way](https://medium.com/@mweststrate/introducing-immer-immutability-the-easy-way-9d73d8f71cb3)
- Short Egghead.io lesson covering the Immer essentials: [Simplify creating immutable data trees with Immer (7m)](https://egghead.io/lessons/redux-simplify-creating-immutable-data-trees-with-immer)
- Free in-depth Egghead.io course: [Immutable JavaScript Data Structures with Immer (58m)](https://egghead.io/courses/immutable-javascript-data-structures-with-immer)
Immer (German for: always) is a tiny package that allows you to work with immutable state in a more convenient way. It is based on the [_copy-on-write_](https://en.wikipedia.org/wiki/Copy-on-write) mechanism.
The basic idea is that you will apply all your changes to a temporary _draftState_, which is a proxy of the _currentState_. Once all your mutations are completed, Immer will produce the _nextState_ based on the mutations to the draft state. This means that you can interact with your data by simply modifying it while keeping all the benefits of immutable data.
Using Immer is like having a personal assistant; he takes a letter (the current state) and gives you a copy (draft) to jot changes onto. Once you are done, the assistant will take your draft and produce the real immutable, final letter for you (the next state).
The interesting thing about Immer is that the `baseState` will be untouched, but the `nextState` will be a new immutable tree that reflects all changes made to `draftState` (and structurally sharing the things that weren't changed).
- Small [](https://img.badgesize.io/https://cdn.jsdelivr.net/npm/immer/dist/immer.umd.js)
