redux

What is redux?

Redux is a predictable state container for JavaScript apps. It helps you write applications that behave consistently, run in different environments (client, server, and native), and are easy to test. Redux provides a single source of truth for your application's state, making state mutations predictable through a strict unidirectional data flow.

What are redux's main functionalities?

State Management

Redux provides a store that holds the state tree of your application. You can dispatch actions to change the state, and subscribe to updates.

const { createStore } = require('redux');

function counter(state = 0, action) {
  switch (action.type) {
    case 'INCREMENT':
      return state + 1;
    case 'DECREMENT':
      return state - 1;
    default:
      return state;
  }
}

let store = createStore(counter);

store.subscribe(() => console.log(store.getState()));

store.dispatch({ type: 'INCREMENT' });
// The current state is 1
store.dispatch({ type: 'INCREMENT' });
// The current state is 2
store.dispatch({ type: 'DECREMENT' });
// The current state is 1

Actions

Actions are payloads of information that send data from your application to your store. They are the only source of information for the store.

function addTodo(text) {
  return {
    type: 'ADD_TODO',
    text
  };
}

store.dispatch(addTodo('Learn Redux'));

Reducers

Reducers specify how the application's state changes in response to actions sent to the store. Remember that actions only describe what happened, but don't describe how the application's state changes.

function todos(state = [], action) {
  switch (action.type) {
    case 'ADD_TODO':
      return state.concat([action.text]);
    default:
      return state;
  }
}

Middleware

Middleware extends Redux with custom functionality. It lets you wrap the store's dispatch method for fun and profit. A very common use is for dealing with asynchronous actions.

const { applyMiddleware, createStore } = require('redux');
const createLogger = require('redux-logger');

const logger = createLogger();
const store = createStore(
  reducer,
  applyMiddleware(logger)
);

Other packages similar to redux

mobx

MobX is a battle-tested library that makes state management simple and scalable by transparently applying functional reactive programming (TFRP). Unlike Redux, which uses a single store and requires you to dispatch actions to change your state, MobX allows you to create multiple stores and uses observables to automatically track changes in state through actions.

vuex

Vuex is a state management pattern + library for Vue.js applications. It serves as a centralized store for all the components in an application, with rules ensuring that the state can only be mutated in a predictable fashion. It is very similar to Redux but is tailored specifically for the Vue.js framework.

flux

Flux is the application architecture that Facebook uses for building client-side web applications. It complements React's composable view components by utilizing a unidirectional data flow. It's more of a pattern rather than a formal framework, and you can start using Flux immediately without a lot of new code. Redux was actually inspired by Flux and can be considered its evolution.

immer

Immer 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 mechanism. The main difference from Redux is that Immer allows you to write code that looks like it's mutating state directly, without actually mutating the state.

README

Redux is a predictable state container for JavaScript apps.
(If you're looking for a WordPress framework, check out Redux Framework.)

It helps you write applications that behave consistently, run in different environments (client, server, and native), and are easy to test. On top of that, it provides a great developer experience, such as live code editing combined with a time traveling debugger.

You can use Redux together with React, or with any other view library.
It is tiny (2kB, including dependencies).

Learn Redux from its creator:
Part 1: Getting Started with Redux (30 free videos)
Part 2: Building React Applications with Idiomatic Redux (27 free videos)

Testimonials

“Love what you're doing with Redux”
Jing Chen, creator of Flux

“I asked for comments on Redux in FB's internal JS discussion group, and it was universally praised. Really awesome work.”
Bill Fisher, author of Flux documentation

“It's cool that you are inventing a better Flux by not doing Flux at all.”
André Staltz, creator of Cycle

Before Proceeding Further

Also read:
You Might Not Need Redux

Developer Experience

I wrote Redux while working on my React Europe talk called “Hot Reloading with Time Travel”. My goal was to create a state management library with minimal API but completely predictable behavior, so it is possible to implement logging, hot reloading, time travel, universal apps, record and replay, without any buy-in from the developer.

Influences

Redux evolves the ideas of Flux, but avoids its complexity by taking cues from Elm.
Whether you have used them or not, Redux only takes a few minutes to get started with.

Installation

To install the stable version:

npm install --save redux

This assumes you are using npm as your package manager.

If you're not, you can access these files on unpkg, download them, or point your package manager to them.

Most commonly people consume Redux as a collection of CommonJS modules. These modules are what you get when you import redux in a Webpack, Browserify, or a Node environment. If you like to live on the edge and use Rollup, we support that as well.

If you don't use a module bundler, it's also fine. The redux npm package includes precompiled production and development UMD builds in the dist folder. They can be used directly without a bundler and are thus compatible with many popular JavaScript module loaders and environments. For example, you can drop a UMD build as a <script> tag on the page, or tell Bower to install it. The UMD builds make Redux available as a window.Redux global variable.

The Redux source code is written in ES2015 but we precompile both CommonJS and UMD builds to ES5 so they work in any modern browser. You don't need to use Babel or a module bundler to get started with Redux.

Complementary Packages

Most likely, you'll also need the React bindings and the developer tools.

npm install --save react-redux
npm install --save-dev redux-devtools

Note that unlike Redux itself, many packages in the Redux ecosystem don't provide UMD builds, so we recommend using CommonJS module bundlers like Webpack and Browserify for the most comfortable development experience.

The Gist

The whole state of your app is stored in an object tree inside a single store.
The only way to change the state tree is to emit an action, an object describing what happened.
To specify how the actions transform the state tree, you write pure reducers.

That's it!

import { createStore } from 'redux'

/**
 * This is a reducer, a pure function with (state, action) => state signature.
 * It describes how an action transforms the state into the next state.
 *
 * The shape of the state is up to you: it can be a primitive, an array, an object,
 * or even an Immutable.js data structure. The only important part is that you should
 * not mutate the state object, but return a new object if the state changes.
 *
 * In this example, we use a `switch` statement and strings, but you can use a helper that
 * follows a different convention (such as function maps) if it makes sense for your
 * project.
 */
function counter(state = 0, action) {
  switch (action.type) {
  case 'INCREMENT':
    return state + 1
  case 'DECREMENT':
    return state - 1
  default:
    return state
  }
}

// Create a Redux store holding the state of your app.
// Its API is { subscribe, dispatch, getState }.
let store = createStore(counter)

// You can use subscribe() to update the UI in response to state changes.
// Normally you'd use a view binding library (e.g. React Redux) rather than subscribe() directly.
// However it can also be handy to persist the current state in the localStorage.

store.subscribe(() =>
  console.log(store.getState())
)

// The only way to mutate the internal state is to dispatch an action.
// The actions can be serialized, logged or stored and later replayed.
store.dispatch({ type: 'INCREMENT' })
// 1
store.dispatch({ type: 'INCREMENT' })
// 2
store.dispatch({ type: 'DECREMENT' })
// 1

Instead of mutating the state directly, you specify the mutations you want to happen with plain objects called actions. Then you write a special function called a reducer to decide how every action transforms the entire application's state.

If you're coming from Flux, there is a single important difference you need to understand. Redux doesn't have a Dispatcher or support many stores. Instead, there is just a single store with a single root reducing function. As your app grows, instead of adding stores, you split the root reducer into smaller reducers independently operating on the different parts of the state tree. This is exactly like how there is just one root component in a React app, but it is composed out of many small components.

This architecture might seem like an overkill for a counter app, but the beauty of this pattern is how well it scales to large and complex apps. It also enables very powerful developer tools, because it is possible to trace every mutation to the action that caused it. You can record user sessions and reproduce them just by replaying every action.

Learn Redux from Its Creator

Getting Started with Redux is a video course consisting of 30 videos narrated by Dan Abramov, author of Redux. It is designed to complement the “Basics” part of the docs while bringing additional insights about immutability, testing, Redux best practices, and using Redux with React. This course is free and will always be.

“Great course on egghead.io by @dan_abramov - instead of just showing you how to use #redux, it also shows how and why redux was built!”
Sandrino Di Mattia

“Plowing through @dan_abramov 'Getting Started with Redux' - its amazing how much simpler concepts get with video.”
Chris Dhanaraj

“This video series on Redux by @dan_abramov on @eggheadio is spectacular!”
Eddie Zaneski

“Come for the name hype. Stay for the rock solid fundamentals. (Thanks, and great job @dan_abramov and @eggheadio!)”
Dan

“This series of videos on Redux by @dan_abramov is repeatedly blowing my mind - gunna do some serious refactoring”
Laurence Roberts

So, what are you waiting for?

Watch the 30 Free Videos!

If you enjoyed my course, consider supporting Egghead by buying a subscription. Subscribers have access to the source code for the example in every one of my videos, as well as to tons of advanced lessons on other topics, including JavaScript in depth, React, Angular, and more. Many Egghead instructors are also open source library authors, so buying a subscription is a nice way to thank them for the work that they've done.

Documentation

• Introduction
• Basics
• Advanced
• Recipes
• FAQ
• Troubleshooting
• Glossary
• API Reference

For PDF, ePub, and MOBI exports for offline reading, and instructions on how to create them, please see: paulkogel/redux-offline-docs.

For Offline docs, please see: devdocs

Examples

• Counter Vanilla (source)
• Counter (source)
• Todos (source)
• Todos with Undo (source)
• TodoMVC (source)
• Shopping Cart (source)
• Tree View (source)
• Async (source)
• Universal (source)
• Real World (source)

If you're new to the NPM ecosystem and have troubles getting a project up and running, or aren't sure where to paste the gist above, check out simplest-redux-example that uses Redux together with React and Browserify.

Discussion

Join the #redux channel of the Reactiflux Discord community.

Thanks

• The Elm Architecture for a great intro to modeling state updates with reducers;
• Turning the database inside-out for blowing my mind;
• Developing ClojureScript with Figwheel for convincing me that re-evaluation should “just work”;
• Webpack for Hot Module Replacement;
• Flummox for teaching me to approach Flux without boilerplate or singletons;
• disto for a proof of concept of hot reloadable Stores;
• NuclearJS for proving this architecture can be performant;
• Om for popularizing the idea of a single state atom;
• Cycle for showing how often a function is the best tool;
• React for the pragmatic innovation.

Special thanks to Jamie Paton for handing over the redux NPM package name.

Logo

You can find the official logo on GitHub.

Change Log

This project adheres to Semantic Versioning.
Every release, along with the migration instructions, is documented on the Github Releases page.

Patrons

The work on Redux was funded by the community.
Meet some of the outstanding companies that made it possible:

• Webflow
• Ximedes

See the full list of Redux patrons., as well as the always-growing list of people and companies that use Redux.

License

MIT