immerjs/immer

What is it?

Key features

• 01Write state updates by mutating a draft instead of copying objects manually.
• 02Produces new immutable state while leaving the original state unchanged.
• 03Core API is a produce function that takes a base state and a recipe.
• 04Distributed as the npm package immer.

Use cases

• Simplifying immutable updates in Redux reducers.
• Updating deeply nested state in React or other UI applications.
• Writing state logic that needs undo history or change tracking through immutable snapshots.

Quick start

1. 1

   Read the documentation at immerjs.github.io/immer to find install instructions

2. 2

   To contribute, open the project in Gitpod, which installs dependencies and runs yarn run start automatically

Topics

FAQ

What is immer?

A JavaScript library that lets you write immutable state updates by mutating a draft copy of the current state. Immer lets developers update immutable state by writing ordinary mutating code. Changes are made to a draft proxy of the current state, and Immer produces a new immutable state tree while leaving the original untouched. This removes the need to manually copy nested objects and arrays when updating state.

Is immer free to use? What license does it have?

immer is open source under the MIT license. Check the license terms before using it in commercial products.

Is immer still maintained?

Actively maintained. The last commit to immer was on Oct 21, 2026.

What can I use immer for?

Simplifying immutable updates in Redux reducers. Updating deeply nested state in React or other UI applications. Writing state logic that needs undo history or change tracking through immutable snapshots.

How do I install immer?

Read the documentation at immerjs.github.io/immer to find install instructions To contribute, open the project in Gitpod, which installs dependencies and runs yarn run start automatically

Where can I get immer?

The source code and installation instructions are on GitHub: https://github.com/immerjs/immer