Skip to content
A TINY, fail-fast, lazy, immutable Javascript objects library.
Branch: master
Clone or download
Fetching latest commit…
Cannot retrieve the latest commit at this time.
Type Name Latest commit message Commit time
Failed to load latest commit information.

immu NPM Module NPM download count Build Status


A TINY, fail-fast, lazy, "naked", simple immutable Javascript objects library.

  • By TINY, less than 1k gzipped and minified.
  • By fail-fast, I mean you'll be notified if you try to change a property.
  • By lazy, I mean it doesn't evaluate the mutability of a property until it absolutely has to.
  • By naked, I mean they work like regular objects and arrays.
  • By simple, I mean that it doesn't add any extra features to your code (except immutability, of course).

What Immu Aims To Solve

Immu aims to solve 2 things:

  1. Immutable javascript Objects (Arrays are objects in Javascript).
  2. Fail-fast errors with detailed exceptions upon attempting to mutate Objects.

Immu does not attempt to add functionality to Arrays, introduce complex data structures like Map and Set, or provide a complete solution with cursors and stores. Immu is meant to be the simplest possible solution to providing immutable objects while maintaining the native API for those objects (including Array methods).

Other libraries that are similar but do more:

Each of these libraries are GREAT in their implementation and at the problems they solve:

Why Use Immutable Data?

Bugs happen because developers write them. This just puts one more layer between you and your code exploding. Immutable data can't promise to help you avoid all bugs, but can help you reason about your state much easier!


npm install immu --save


'use strict';

let immu = require('immu');

let user = {
  name: 'Scott',
  age: 31,
  location: 'somewhere'

let immutableUser = immu(user);

try { = 'Unchangeable';
catch (e) {
  console.error(e.message); // Cannot change value of an immutable property

console.log( // Scott

// Get the raw object back
console.log(immutableUser.toJS()); // {name: 'Scott', age: 31, location: 'somewhere'}

let list = immu([1, 2, 3, 4]);
let newList = list
  .map(item => item + 1)
  .filter(item => item % 2 === 0);
console.log(Array.isArray(list)) // true

Run Tests

git clone && cd immu
npm install
npm test
You can’t perform that action at this time.