Learn how to Use Redux to Manage your Application State

Redux is a popular state management library that is commonly used with React applications, although it can be used with other technologies as well. This guide will provide a simple and easy-to-follow overview of Redux and how to use it effectively.

Why you need Redux

Redux provides a way to manage the state of your application by moving it to an external global store. While React has its own method for managing state, Redux becomes necessary for complex applications where you find yourself moving state up and down the component tree using props.

It’s important to note that with React version 16.3.0, the Context API was introduced which made Redux less necessary for accessing state from different parts of your app. In such cases, consider using the Context API instead, unless you require specific features provided by Redux.

When should you use Redux?

Redux is best suited for medium to large-sized applications. It should only be used when the default state management of React or your chosen library is no longer sufficient. Simple applications may not require Redux at all, and there’s nothing wrong with that.

Immutable State Tree

In Redux, the entire state of your application is represented by a single JavaScript object called the “State” or “State Tree”. We refer to it as an “Immutable State Tree” because it cannot be changed directly. Instead, it can only be changed by dispatching an action.

Actions

Actions in Redux are JavaScript objects that describe a change in the state of your application in a minimal way. They typically have a “type” property which is usually a string. For example:

{
  type: 'CLICKED_SIDEBAR'
}

// With additional data
{
  type: 'SELECTED_USER',
  userId: 232
}

It is recommended to use constants to define action types, especially as your application grows. You can create action creators, which are functions that create actions. For example:

const ADD_ITEM = 'ADD_ITEM';

function addItem(t) {
  return {
    type: ADD_ITEM,
    title: t
  }
}

You can then dispatch these actions in combination with the dispatcher or define your own action dispatcher function. Reducers are responsible for handling these actions.

Reducers

Reducers in Redux are pure functions that calculate the next state tree based on the previous state tree and the action that was dispatched. They follow certain rules to ensure consistency and maintainability:

A reducer should never mutate its arguments or the state directly. Instead, create a new state object using Object.assign({}, ...).
A reducer should not generate side effects, such as making API calls or calling non-pure functions.
Reducers are used to handle specific types of actions, so in a complex app, you may have multiple reducers for different parts of the state.

A simple simulation of a reducer can be described using an example state, a list of actions, and separate reducers for different parts of the state. Finally, a reducer can be created to handle the entire state. For more complex apps, you may need to design multiple reducers.

The Store

The Store in Redux is an object that holds the state of your application. It exposes the state via getState(), allows you to update the state via dispatch(), and enables you to listen to state changes using subscribe().

Each application should have a unique store. Creating a store involves importing the createStore function from Redux and passing in the root reducer. For example:

import { createStore } from 'redux';
import rootReducer from './reducers';
let store = createStore(rootReducer);

The store can be initialized with server-side data by passing a starting state as a parameter:

let store = createStore(rootReducer, preexistingState);

You can retrieve the current state of the store using store.getState() and update the state using store.dispatch(). Additionally, you can listen to state changes with store.subscribe().

Data Flow

Data flow in Redux is unidirectional. When an action is dispatched using store.dispatch(), the store passes the action to the relevant reducer, which calculates the next state tree. The store then updates the state and notifies all subscribed listeners.

By understanding the core principles of Redux, you can effectively manage the state of your application and improve the overall performance and maintainability of your codebase.

Why you need Redux#

When should you use Redux?#

Immutable State Tree#

Actions#

Reducers#

The Store#

Data Flow#