Persistent, immutable data structures for JavaScript / TypeScript

List Map Set Record and a lazy Seq — highly efficient, with zero dependencies and TypeScript types in the box.

Read the docs Try it in the browser

$ npm install immutable

The collection family

Several persistent collections, one familiar API

Ordered, indexed — like Array

Keyed pairs, keys of any type

Unique values by equality

Typed keyed structures

Map that keeps insertion order

Set that keeps insertion order

LIFO, fast prepend

Lazy — plus Range & Repeat

Why Immutable.js

Built to make data simpler and faster

Performance

Fast & memory-light

New versions reuse the parts that didn't change — cheap to create, and the original is never touched. No defensive copying.

Lazy Seq

Chaining without cost

Chain map, filter and more — even over infinite ranges — with zero intermediate arrays.

State

Simpler application state

Data never mutates under you, so undo/redo, change detection and memoization become trivial. A natural fit for React & Redux.

fromJS / toJS

Interop with plain JS

Convert to and from objects & arrays, shallow or deep, in a single call.

getIn / setIn / updateIn

Deep, without the pain

Read and update values buried deep in nested structures with a path.

TypeScript

Typed out of the box

First class TypeScript support: full generics, error detection and editor auto-complete — nothing to install.

Examples

Build & transform a List — every call returns a new List

const upperFirst = (str) =>
  str.charAt(0).toUpperCase() + str.slice(1);

List(['apple', 'banana', 'coconut'])
  .push('dragonfruit')
  .map((fruit) => upperFirst(fruit));
// → List [ "Apple", "Banana", "Coconut", "Dragonfruit" ]

Live & editable

Every example runs, right here

Edit the code and press Run. No install, no setup — the same interactive editor appears throughout the docs so you can learn by trying.

Open the full Playground →