Understanding Redux: A tutorial with examples

Editor’s note: This React Redux tutorial was last updated on 11 September 2023 to update code blocks.

In the ever-evolving world of web development, new JavaScript libraries are always being released. But chasing after each new release without fully understanding their benefits isn’t a good idea.

Redux is an example of a JavaScript library whose enduring popularity is a testament to its value. In this guide, we’ll provide a foundational understanding of Redux, highlighting its functionalities and why you should use it. We’ll explore its benefits by using a simple but practical component.

Jump ahead:

• An introduction to Redux
• When to use Redux
• What is Redux used for?
• Using Redux with React
• State management with Redux
• How Redux works
  • Redux actions
  • Redux reducers
  • Redux store
  • Redux toolkit
• Redux middleware
• Benefits of using Redux
  • • Redux makes the state predictable
    • Redux is maintainable
  • Debugging is easy in Redux
  • Performance benefits
  • Ease of testing
  • State persistence
  • Server-side rendering

An introduction to Redux

Redux is a predictable state container designed to help you write JavaScript apps that behave consistently across client, server, and native environments, and are easy to test.

While it’s mostly used as a state management tool with React, you can use Redux with any other JavaScript framework or library. It’s lightweight at 2KB (including dependencies), so you don’t have to worry about it making your application’s asset size bigger.

With Redux, the state of your application is kept in a store, and each component can access any state that it needs from this store. If you’re just getting started with Redux, this video is a great resource for beginners.

When to use Redux

Not long after its release, Redux became one of the hottest topics of debate in the frontend world.

Redux allows you to manage your app’s state in a single place and keep changes in your app more predictable and traceable, making it easier to understand the changes happening in your app. But all of these benefits come with a set of challenges. Some developers argue that Redux introduces unnecessary boilerplate, potentially complicating what are otherwise simple tasks. However, this depends on the architectural decisions of the project.

So, when should you use Redux? One simple answer to this question is that you will organically realize for yourself when you need Redux. If you’re unsure about whether you need it, you probably don’t. This usually happens when your app grows to a scale where managing app state becomes a hassle and you start looking for ways to make it simplify it.

What is Redux used for?

Redux is used to maintain and update data across your applications for multiple components to share, all while remaining independent of the components.

In a large application, there is a need to store the state at a central location and share it among the different components. That is where the Redux store comes into the picture:

If the data needs to be passed from a parent to a child deep down the tree, this can still be accomplished using React utilities like Context. But when it comes to sharing the state between components on the same level, Redux is the inevitable option.

Using Redux with React

As we mentioned earlier, Redux is a standalone library that can be used with different JavaScript frameworks including Angular, Inferno, Vue, Preact, React, etc. However, Redux is most frequently used with React.

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This is because React only allows for a uni-directional flow of data. That means data cannot be sent from a child to a parent; it has to flow downward from the parent to the child. This thought model works very well with Redux where we cannot directly modify the state. Instead, we dispatch actions that intend to change the state, and then separately, we observe the resulting state changes.

State management with Redux

State management is essentially a way to facilitate the communication and sharing of data across components. It creates a tangible data structure to represent the state of your app that you can read from and write to. That way, you can see otherwise invisible states while you’re working with them.

Most libraries, such as React and Angular, are built with a way for components to internally manage their state without the need for an external library or tool. This works well for applications with few components, but as an application grows larger, managing states shared across components becomes a hassle.

In an app where data is shared among components, it might be confusing to actually know where a state should live. Ideally, the data in a component should live in just one component, so sharing data among sibling components becomes difficult.

For example, to share data among siblings in React, a state has to live in the parent component. A method for updating this state is provided by the parent component and passed as props to these sibling components.

Here’s a simple example of a login component in React. The input of the login component affects what is displayed by its sibling component, the status component:

import React, { useState } from 'react';

const App = () => {
  const [count, setCount] = useState(0);

  const handleIncrement = (incrementBy) => {
    const numberToIncrement = incrementBy || 1;
    setCount(count + numberToIncrement)
  }

  return (
    <div>
      <BigCountDisplay count={count} />
      <CounterButton onIcrement={handleIncrement} />
    </div>
  );
}

export default App;

Remember, this data is not needed by the parent component, but because its children need to share data, it has to provide a state.

Now imagine what happens when a state has to be shared between components that are far apart in the component tree. Basically, the state will have to be lifted up to the nearest parent component and upwards until it gets to the closest common ancestor of both components that need the state, and then it is passed down. This makes the state difficult to maintain and less predictable.

It’s clear that state management gets messy as the app gets more complex. This is why you need a state management tool like Redux to more easily maintain these states. Now, let’s take a look at Redux concepts before considering its benefits.

How Redux works

The way Redux works is simple. There is a central store that holds the entire state of the application. Each component can access the stored state without having to send down props from one component to another.

There are three core components in Redux — actions, store, and reducers. Let’s briefly discuss what each of them does. This is important because they help you understand the benefits of Redux and how it can be used.

We’ll be implementing a similar example to the login component above but this time in Redux.

💡 store refers to the object that holds the application data shared between components.

Redux actions

Redux actions are events. They are the only way you can send data from your application to your Redux store. The data can be from user interactions, API calls, or even form submissions.

Actions are plain JavaScript objects that must have:

• A type property to indicate the type of action to be carried out
• A payload object that contains the information that should be used to change the state

Actions are created via an action creator, which is a function that returns an action. Actions are executed using the dispatch() method, which sends the action to the store:

Here’s an example of an action:

{ 
  type: "INCREMENT",
  payload: {
    incrementBy: 5,
  }
}

And here is an example of an action creator. It is just a helper function that returns the action:

const getIncrementAction = (numberToIncrement) => {
  return {
    type: "INCREMENT",
    payload: {
      incrementBy: numberToIncrement,
    }
  }
}

Redux reducers

Reducers are pure functions that take the current state of an application, perform an action, and return a new state. The reducer handles how the state (application data) will change in response to an action:

💡 A pure function is a function that will always return the same value if given the same parameters, i.e., the function depends on only the parameters and no external data.

Reducers are based on the reduce function in JavaScript, where a single value is calculated from multiple values after a callback function has been carried out.

Here is an example of how reducers work in Redux:

const CounterReducer = (state = initialState, action) => {
    switch (action.type) {
      // This reducer handles any action with type "LOGIN"
      case "INCREMENT":
          return state + action.incrementBy ? action.incrementBy : 1
       default:
          return state;
      } 
};

Hence, if the initial state was 12, after the action to increment it by five gets dispatched and processed, we get the new value of the state, i.e., 17.

💡 Reducers take the previous state of the app and return a new state based on the action passed to it. As pure functions, they do not change the data in the object passed to them or perform any side effect in the application. Given the same object, they should always produce the same result.

Redux store

The store is a “container” (really, a JavaScript object) that holds the application state, and the only way the state can change is through actions dispatched to the store. Redux allows individual components to connect to the store.

It is highly recommended to keep only one store in any Redux application. You can access the stored state, update the state, and register or unregister listeners via helper methods. Basically, the components get to update the store via actions and then subscribe to the changes to the store so they know when to re-render:

Redux toolkit

Redux is a great utility for state management in React. But, as we mentioned before, it can introduce a lot of boilerplate into your application due to the verbosity of its API. Because of this, it is recommended to use the Redux Toolkit while using Redux with React. Let’s look at a few benefits that this provides.

Setting up a store with Redux toolkit

While setting up a store with pure Redux can be quite cumbersome, with Redux Toolkit, it is a single call to the configureStore function. This is how we can set up a store that has a counterReducer slice in it:

import { configureStore } from '@reduxjs/toolkit'
import counterReducer from './counterReducer'

const store = configureStore({
  reducer: {
    counter: counterReducer,
  },
})

export default store

Creating an action using Redux Toolkit

Redux Toolkit also provides us with utilities to generate actions. In Redux, actions are just normal objects with a type and a payload field. The createAction utility from Redux Toolkit returns us a function. We can call that function with any object and it will get dispatched as the payload for that particular action:

const addTodo = createAction('INCREMENT')
addTodo({ val: 5 })
// {type : "INCREMENT", payload : {val : 5}})

Creating the reducer with Redux Toolkit

The reducer in Redux is a normal, pure function that takes care of the various possible values of state using the switch case syntax. But that means several things need to be taken care of — most importantly, keeping the state immutable.

Redux Toolkit provides the createReducer utility, which internally uses immer. This allows us to freely mutate the state, and it will internally be converted to an immutable version. This is how a reducer defined with Redux Toolkit would look like:

import { createAction, createReducer } from '@reduxjs/toolkit'

const increment = createAction('counter/increment')
const incrementByAmount = createAction('counter/incrementByAmount')

const initialState = { value: 0 }

const counterReducer = createReducer(initialState, (builder) => {
  builder
    .addCase(increment, (state, action) => {
      state.value++
    })
    .addCase(incrementByAmount, (state, action) => {
      state.value += action.payload
    })
})

Notice how easy that makes the task of playing with the state. The difference is more evident when the state is more complex with several nested objects. In the scenario without Redux Toolkit, we have to be careful to keep all the operations immutable but the equivalent code with Toolkit is much more simplified:

// a case without toolkit, notice the .map to create a new state
case 'TOGGLE_TODO': {
  const { index } = action.payload
  return state.map((todo, i) => {
    if (i !== index) return todo

    return {
      ...todo,
      completed: !todo.completed,
    }
  })
}

// a case with toolkit, notice the mutation which is taken care internally
.addCase('TOGGLE_TODO', (state, action) => {
  const todo = state[action.payload.index]
  // "mutate" the object by overwriting a field
  todo.completed = !todo.completed
})

With that in place, let’s now move to learning about what Redux middleware are and how they can further simplify the overall experience.

Redux middleware

Redux allows developers to intercept all actions dispatched from components before they are passed to the reducer function. This interception is done via middleware, which are functions that call the next method received in an argument after processing the current action.

Here’s what a simple middleware looks like:

function simpleMiddleware({ getState, dispatch }) {
  return function(next){
    return function(action){
      // processing
      const nextAction = next(action);
      // read the next state
      const state = getState();
      // return the next action or you can dispatch any other action
      return nextAction;  
    }
  }
}

This might look overwhelming, but in most cases, you won’t need to create your own middleware because the Redux community has already made many of them available. If you feel middleware is required, you will appreciate its capacity to enable great work with the best abstraction.

Benefits of using Redux

When using Redux with React, states will no longer need to be lifted up. This makes it easier for you to trace which action causes any change.

As you can see in the example above, the component does not need to provide any state or method for its children components to share data among themselves. Everything is handled by Redux, which greatly simplifies the app and makes it easier to maintain.

This is the primary reason why you should use Redux, but it’s not the only benefit. Take a look at the list below for a summary of what you stand to gain by using Redux for state management.

Redux makes the state predictable

In Redux, the state is always predictable. If the same state and action are passed to a reducer, the same result is always produced because reducers are pure functions. The state is also immutable, which makes it possible to implement difficult tasks like infinite undo and redo. It is also possible to implement time travel — that is, the ability to move back and forth among the previous states and view the results in real time.

Redux is maintainable

Redux is strict about how code should be organized, which makes it easier for someone with knowledge of Redux to understand the structure of any Redux application. This generally makes it easier to maintain, and also helps you segregate your business logic from your component tree. For large scale apps, it’s critical to keep your app more predictable and maintainable.

Debugging is easy in Redux

Redux makes it easy to debug an application. By logging actions and state, it is easy to understand coding errors, network errors, and other forms of bugs that might come up during production.

Besides logging, it has great DevTools that allow you to time travel actions, persist actions on page refresh, and more.

For medium- and large-scale apps, debugging takes more time then actually developing features. Redux DevTools makes it easy to take advantage of all Redux has to offer.

Performance benefits

You might assume that keeping the app’s state global would result in some performance degradation. To a large extent, that’s not the case. React Redux implements many performance optimizations internally so that your own connected component only re-renders when it actually needs to.

Ease of testing

It is easy to test Redux apps because they rely on pure functions. This means tht tests can simply call a pure function with specific parameters and check if the return value matches the expected result.

State persistence

With Redux, you can persist some of the app’s state to localStorage and restore it after a refresh.

Server-side rendering

Redux can also be used for server-side rendering. With it, you can handle the initial render of the app by sending the state of an app to the server along with its response to the server request. The required components are then rendered in HTML and sent to the clients.

Conclusion

In this guide, we discussed the major features of Redux and how Redux can be beneficial to your app. While Redux has many helpful features, that does not mean you should add Redux to all of your apps. It’s important to know when and when not to use Redux.

One major benefit of Redux is the ability to navigate through the state’s history, allowing developers to observe how the state has changed throughout the app’s lifecycle. However, it is important to implement Redux only if it fits your requirements and your project needs a state management tool.