Next.js SSR: How It Works

Next.js SSR: How It Works


2 min read

Next.js is a powerful React framework that provides several features to enhance your web development experience. One of these features is Server Side Rendering (SSR), 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 SSR works.

The Basics of SSR

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.

Server Side Rendering (SSR) solves this problem by rendering the React components on the server and sending the resulting HTML to the client. The page is immediately interactive, even before all the JavaScript has loaded.

The Process of SSR 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 SSR process.

Data Fetching

Next.js calls a special function called getServerSideProps(). This function runs on the server 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.

Component Rendering

Next.js renders the React components on the server using the data returned by getServerSideProps(). 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.

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.

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.


Next.js SSR is a powerful feature that can greatly improve your web application’s performance and user experience. By rendering pages on the server, 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 SSR can improve performance, it also adds complexity to your application and increases server load. Therefore, it’s important to consider whether SSR is necessary for each page in your application.

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

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