How to Connect React to Redux: A Diagrammatic Guide

React and Redux are two of the most popular tools for building modern web applications. While React excels at building interactive UIs by breaking them into reusable components, Redux provides a centralized way to manage application state that is more predictable and easier to reason about. Connecting React components to the Redux store allows your UI to stay in sync with your state as it changes over time.

In this guide, we‘ll walk through exactly how React and Redux fit together, aided by helpful diagrams to visualize the flow of data between them. By the end, you‘ll have a solid understanding of the core concepts and techniques needed to build a well-architected React-Redux application. Let‘s get started!

Understanding the Roles of React and Redux

Before we dive into connecting React and Redux, let‘s briefly review what each one does on its own:

React is a library for building composable UI components. It lets you define the visual appearance of your app as a function of its current state. When the state changes, React automatically updates the components that depend on it.

Redux is a library for managing global application state. It provides a centralized store that holds the entire state of your app. The store is the single source of truth and can only be modified by dispatching actions to it. Reducers specify how the state should change in response to those actions.

The key idea of using React and Redux together is that you can extract your state management code from your UI components and put it in a separate place – the Redux store. Your components simply declare what data they need from the store and how they want to change it. This keeps them more focused and reusable.

The Redux Data Flow

To understand how data flows between React components and the Redux store, it‘s helpful to visualize the Redux architecture:

As shown in the diagram above, there are several key parts of the Redux data flow:

1. Store – Holds the global state of the application. Can only be modified by dispatching actions to it.

2. Action – A plain JavaScript object that describes a change you want to make to the state. Must have a ‘type‘ property.

3. Reducer – A pure function that takes the current state and an action, decides how to update the state if necessary, and returns the next state.

4. View – The UI layer, built with React components. Renders the data from the current state and triggers actions based on user input.

One of the core ideas of Redux is that the data flows in a single direction:

1. State describes the condition of the app at a point in time
2. The UI is rendered based on that state
3. When something happens (e.g. user clicks a button), the state is updated via actions
4. The UI re-renders based on the new state

This predictable, unidirectional flow makes it easier to understand how your application works as it grows in size and complexity. It‘s always clear where the data is coming from and how it changes over time.

Connecting React Components to Redux

Now that we understand how data flows through a Redux app, let‘s look at how to actually connect your React components to the Redux store so they can access the state and dispatch actions to modify it.

Redux itself is UI-agnostic, so it doesn‘t care what library you use to build your interface. However, the react-redux library provides a set of bindings to make it easy to use Redux with React.

At the core of react-redux are two key components:

1. Provider – Makes the Redux store available to the rest of your app. Wraps your root component.

2. connect – Creates a wrapper component around your React component that maps parts of the Redux state and actions to your component‘s props.

Here‘s a diagram showing how the Provider and connect fit into the React-Redux architecture:

Let‘s walk through the steps to connect a React component to the Redux store:

1. Wrap your root React component with the Provider component from react-redux, passing it your Redux store:

import React from ‘react‘ 
import { render } from ‘react-dom‘
import { Provider } from ‘react-redux‘
import store from ‘./store‘
import App from ‘./App‘

render(
  <Provider store={store}>
    <App />
  </Provider>,
  document.getElementById(‘root‘)
)

2. In your component file, import connect from react-redux:

import { connect } from ‘react-redux‘

3. Define a mapStateToProps function that specifies which pieces of the Redux state you want to pass to your component as props:

const mapStateToProps = state => ({
  products: state.products,
  currentUser: state.currentUser
})

4. Define a mapDispatchToProps object that contains the actions you want to be able to dispatch from your component:

const mapDispatchToProps = {
  addToCart: addToCart,
  removeFromCart: removeFromCart  
}

5. Pass your component and these two mapping functions to connect:

export default connect(
  mapStateToProps,
  mapDispatchToProps
)(MyComponent)

This will create a new wrapper component that renders your original component with the props from mapStateToProps and mapDispatchToProps merged into its props.

Here‘s a simplified example component showing how you can access Redux state and actions after connecting:

import React from ‘react‘
import { connect } from ‘react-redux‘ 
import { addToCart } from ‘../actions‘

const ProductItem = ({ product, addToCart }) => {
  return (
    <div>
      <h3>{ product.name }</h3>
      <button onClick={() => addToCart(product)}>
        Add to Cart
      </button>
    </div>
  )
}

const mapStateToProps = (state, ownProps) => ({
  product: state.products.find(p => p.id === ownProps.id)  
})

export default connect(mapStateToProps, { addToCart })(ProductItem)

In this example, the ProductItem component receives the product it needs to render from the Redux store via mapStateToProps, and the addToCart action via mapDispatchToProps. When the button is clicked, it dispatches the addToCart action to update the store.

Putting It All Together

We‘ve covered a lot! Let‘s review the key steps in building a React-Redux app:

1. Design the shape of your state and create initial reducers
2. Create your Redux store with createStore, passing your root reducer
3. Wrap your root React component with , passing it the store
4. Connect individual components with connect and mapStateToProps/mapDispatchToProps
5. Access Redux state and actions in your components to render your UI and dispatch actions

Following this architecture allows you to manage the complexities of application state in a scalable and maintainable way. The unidirectional flow of data and separation of concerns between presentational and container components keeps your app predictable as it grows.

Debugging and Best Practices

While React-Redux provides a solid foundation for building complex UIs, there are still some common pitfalls to watch out for and best practices to follow:

• Make sure you follow the rules of reducers: keep them pure and have them update state immutably. This makes your app more predictable and enables useful features like "time-travel debugging".

• Use selectors to encapsulate state shape logic. Selectors are functions that take the state as an argument and return some data from it. They help decouple your components from the shape of the state, making refactoring easier.

• Avoid putting non-serializable values like functions or promises into your state or actions. This breaks features like time-travel debugging and persistence. Use sagas or thunks to encapsulate async logic instead.

• Use the Redux DevTools extension to debug your app. It lets you inspect every state and action, and "time-travel debug" – moving back and forth among the actions you‘ve dispatched.

• Consider using a library like Reselect to create memoized "selector" functions. This can help improve performance by avoiding unnecessary re-renders when the state changes but the data your component needs does not.

Conclusion

Connecting React and Redux is a powerful way to build complex yet maintainable web applications. By visualizing how data flows through your app with the help of diagrams, and following best practices around designing actions and reducers, you can create an architecture that is both scalable and easy to reason about.

While there is an initial learning curve to putting all the pieces together, the long-term benefits are well worth it. Having a solid grasp of React-Redux will equip you to build modern, responsive UIs that can smoothly handle the state management needs of today‘s web apps.