Next.js CSR: How It Works

Next.js CSR: How It Works


3 min read

Next.js is a powerful React framework that provides several features to enhance your web development experience. One of these features is Client Side Rendering (CSR), which can significantly improve the performance of your web applications and provide a better user experience. In this article, we will delve deeper into how Next.js CSR works.

The Basics of CSR

In a traditional Single Page Application (SPA), the server sends an HTML file with a JavaScript bundle to the client. The JavaScript then takes over and hydrates the page to add event listeners and manage state. This process can lead to a delay in interactivity, especially for users with slow network connections.

Client Side Rendering (CSR) solves this problem by rendering the React components on the client side. The page is immediately interactive, even before all the JavaScript has loaded.

The Process of CSR in Next.js

When a request is made to a Next.js server, it first checks if there is a static HTML version of the page in the cache. If it exists, it sends that to the client. If not, it proceeds with the CSR process.

Data Fetching

Next.js calls a special function called getInitialProps(). This function runs on the client side and can be used to fetch any data that the page needs to render. This could be data from an API, a database, or any other source.

The getInitialProps() function is asynchronous, meaning it can use the await keyword to wait for promises to resolve. This is particularly useful when fetching data from an API, as it allows the function to wait for the data to be retrieved before continuing.

Component Rendering

Next.js renders the React components on the client side using the data returned by getInitialProps(). It generates an HTML document with this rendered content. This process involves calling the renderToString() function from react-dom/server, which turns React components into HTML strings.

The renderToString() function takes a React element and returns an HTML string that represents that element. This string is then inserted into the HTML document that is sent to the client.

Response Sending

The server sends this HTML document to the client along with minimal JavaScript code for interactivity. The page appears almost instantly and is interactive even before all JavaScript has loaded.

The minimal JavaScript code sent with the HTML document includes event handlers for user interactions such as clicks and form submissions. It also includes code to manage state and update the DOM when state changes.

Page Hydration

Once all JavaScript has loaded, React “hydrates” the page. This means it attaches event listeners and sets up any additional interactivity that couldn’t be captured in the HTML alone.

Hydration involves replacing server-rendered static markup with fully interactive components. During hydration, React will preserve all of the existing DOM nodes, attach event listeners, and update any dynamic content.


Next.js CSR is a powerful feature that can greatly improve your web application’s performance and user experience. By rendering pages on the client side, it ensures that users can see and interact with your pages as quickly as possible, regardless of their network speed or device capabilities.

Remember, while CSR can improve performance, it also adds complexity to your application and increases server load. Therefore, it’s important to consider whether CSR is necessary for each page in your application.

I hope this article helps you understand how Next.js CSR works in depth!

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