Writing Tests Because most of the Redux code you write are functions, and many of them are pure, they are easy to test without mocking. Setting Up We recommend Jest as the testing engine. Note that it runs in a Node environment, so you won't have access to the DOM. npm install --save-dev jest To use it together with Babel, you will need to install babel-jest: npm install --save-dev babel-jest and configure it to use ES2015 features in .babelrc: { "presets": ["es2015"] } Then, add this to scri

Using Object Spread Operator Since one of the core tenets of Redux is to never mutate state, you'll often find yourself using Object.assign() to create copies of objects with new or updated values. For example, in the todoApp below Object.assign() is used to return a new state object with an updated visibilityFilter property: function todoApp(state = initialState, action) { switch (action.type) { case SET_VISIBILITY_FILTER: return Object.assign({}, state, { visibilityFilter:

Using combineReducers Core Concepts The most common state shape for a Redux app is a plain Javascript object containing "slices" of domain-specific data at each top-level key. Similarly, the most common approach to writing reducer logic for that state shape is to have "slice reducer" functions, each with the same (state, action) signature, and each responsible for managing all updates to that specific slice of state. Multiple slice reducers can respond to the same action, independently update t

Usage with React Router So you want to do routing with your Redux app. You can use it with React Router. Redux will be the source of truth for your data and React Router will be the source of truth for your URL. In most of the cases, it is fine to have them separate unless if you need to time travel and rewind actions that triggers the change URL. Installing React Router react-router is available on npm . This guides assumes you are using react-router@^2.7.0. npm install --save react-router Con

Usage with React From the very beginning, we need to stress that Redux has no relation to React. You can write Redux apps with React, Angular, Ember, jQuery, or vanilla JavaScript. That said, Redux works especially well with libraries like React and Deku because they let you describe UI as a function of state, and Redux emits state updates in response to actions. We will use React to build our simple todo app. Installing React Redux React bindings are not included in Redux by default. You need

Troubleshooting This is a place to share common problems and solutions to them. The examples use React, but you should still find them useful if you use something else. Nothing happens when I dispatch an action Sometimes, you are trying to dispatch an action, but your view does not update. Why does this happen? There may be several reasons for this. Never mutate reducer arguments It is tempting to modify the state or action passed to you by Redux. Don't do this! Redux assumes that you never mut

Three Principles Redux can be described in three fundamental principles: Single source of truth The state of your whole application is stored in an object tree within a single store. This makes it easy to create universal apps, as the state from your server can be serialized and hydrated into the client with no extra coding effort. A single state tree also makes it easier to debug or introspect an application; it also enables you to persist your app's state in development, for a faster developm

Structuring Reducers At its core, Redux is really a fairly simple design pattern: all your "write" logic goes into a single function, and the only way to run that logic is to give Redux a plain object that describes something that has happened. The Redux store calls that write logic function and passes in the current state tree and the descriptive object, the write logic function returns some new state tree, and the Redux store notifies any subscribers that the state tree has changed. Redux put

subscribe(listener) Adds a change listener. It will be called any time an action is dispatched, and some part of the state tree may potentially have changed. You may then call getState() to read the current state tree inside the callback. You may call dispatch() from a change listener, with the following caveats: The listener should only call dispatch() either in response to user actions or under specific conditions (e. g. dispatching an action when the store has a specific field). Calling di

replaceReducer(nextReducer) Replaces the reducer currently used by the store to calculate the state. It is an advanced API. You might need this if your app implements code splitting, and you want to load some of the reducers dynamically. You might also need this if you implement a hot reloading mechanism for Redux. Arguments reducer (Function) The next reducer for the store to use.