Understanding React: SSR vs CSR vs ISR

React is a popular JavaScript library for building user interfaces, especially single-page applications (SPAs). When leveraging React, developers often encounter three distinct rendering techniques: Server-Side Rendering (SSR), Client-Side Rendering (CSR), and Incremental Static Regeneration (ISR). Each method has its own merits and use cases, which we’ll explore in this article to help you make informed decisions in your web development projects.

What is Server-Side Rendering (SSR)?

Server-Side Rendering (SSR) is a web application architecture where the server processes the application’s content, generates HTML, and sends it to the client. This means that for every request made, the server compiles the React components into HTML. SSR can be beneficial for SEO and initial load times, as it allows search engines to view and index page content easily.

How SSR Works

When a user requests a page, the following process occurs:

1. The server receives the request.
2. The server runs the application code and generates the required HTML.
3. The HTML is sent back to the client, which is then displayed in the browser.
4. Once the HTML is loaded, the React application “hydrates,” attaching event listeners for interactivity.

Benefits of SSR

• Improved SEO: Since search engines receive fully rendered HTML, content is indexed more effectively.
• Faster Initial Load: Users see the page content promptly, even before all JavaScript is fully executed.
• Better Performance on Low-End Devices: Rendering on the server can relieve the client’s processing load.

Drawbacks of SSR

• Server Load: Each request to the server generates a new instance of the application, which can lead to higher server load.
• Slower Navigation: Navigating between pages usually requires additional requests to the server.

SSR Example with Next.js

Next.js is a framework built on top of React that simplifies SSR implementation. Here’s a basic example:

import React from 'react';
import fetch from 'isomorphic-unfetch';

const Users = ({ users }) => {
    return (
        

            {users.map(user => (
                
{user.name}
            ))}
        
    );
};

Users.getInitialProps = async () => {
    const res = await fetch('https://jsonplaceholder.typicode.com/users');
    const users = await res.json();
    return { users };
};

export default Users;

What is Client-Side Rendering (CSR)?

Client-Side Rendering (CSR), in contrast, dynamically generates web content in the browser using JavaScript. With CSR, the server sends a minimal HTML shell with JavaScript files, which the browser executes to render the application on the client side. This approach is typical for SPAs.

How CSR Works

Here’s a simplified flow of CSR:

1. The server sends the initial HTML and JavaScript bundles to the client.
2. The browser downloads and executes the JavaScript files.
3. The React application takes over, generating the UI dynamically.

Benefits of CSR

• Rich Interactivity: The application feels more interactive and responsive since re-rendering does not require contacting the server.
• Reduced Server Load: Once loaded, subsequent interactions are client-side without needing to involve the server.
• Simplified Development: Handling routing and state management is often easier within the client application.

Drawbacks of CSR

• SEO Challenges: Search engines might not index the content effectively since the initial page load contains little to no meaningful content.
• Slower Initial Load Times: Users may initially see a blank page while JavaScript loads before rendering content.

CSR Example with React

A basic example of a CSR application is illustrated below:

import React, { useEffect, useState } from 'react';

const Users = () => {
    const [users, setUsers] = useState([]);

    useEffect(() => {
        const fetchUsers = async () => {
            const res = await fetch('https://jsonplaceholder.typicode.com/users');
            const data = await res.json();
            setUsers(data);
        };
        fetchUsers();
    }, []);

    return (
        

            {users.map(user => (
                
{user.name}
            ))}
        
    );
};

export default Users;

What is Incremental Static Generation (ISR)?

Incremental Static Regeneration (ISR) is a hybrid approach that allows developers to build pages statically, and then revalidate the content at specified intervals or on-demand. ISR is an excellent balance between SSR and traditional static site generation.

How ISR Works

ISR preserves the benefits of static generation and allows pages to be updated on the fly:

1. When a user visits a page, the server checks if the static version is available.
2. If it exists, it serves the static page; if not, it generates it on demand.
3. Once the static page is served, a timer counts down a specified duration for subsequent regeneration.

Benefits of ISR

• SEO-Friendly: Like SSR, it serves pre-rendered HTML for improved indexing.
• Performance: Users experience high-speed delivery of static pages.
• On-Demand Updates: Content can be updated frequently without a full rebuild of the site.

Drawbacks of ISR

• Cache Invalidation Complexity: Managing cache and content freshness can be complex.
• Requires Framework Support: Not all frameworks natively support ISR; Next.js does.

ISR Example with Next.js

Here is a simple example of ISR using Next.js:

import React from 'react';
import fetch from 'isomorphic-unfetch';

const Users = ({ users }) => {
    return (
        

            {users.map(user => (
                
{user.name}
            ))}
        
    );
};

// This function fetches data at the time of the request
export async function getStaticProps() {
    const res = await fetch('https://jsonplaceholder.typicode.com/users');
    const users = await res.json();
    return {
        props: { users },
        revalidate: 10, // re-generate the page at most every 10 seconds
    };
}

export default Users;

When to Use SSR, CSR, and ISR

The choice between SSR, CSR, and ISR depends on the specific needs of your project:

• Use SSR: When SEO is critical, and you want fast initial load times, such as in blogs, marketing sites, or e-commerce product pages.
• Use CSR: For applications focusing on user interactivity, such as social media platforms or web apps, where SEO is not a primary concern.
• Use ISR: For content-driven sites that need a balance of static performance with the ability to refresh content without a full rebuild, like news sites or documentation.

Conclusion

Understanding the differences between SSR, CSR, and ISR is essential for web developers aiming to build efficient, user-friendly applications. Each approach has its own set of advantages and trade-offs, and the choice ultimately relies on the specific requirements of the project at hand. By leveraging React efficiently, you can significantly enhance your application’s performance and user experience.

Explore these strategies more in-depth, experiment with them, and find the best fit for your next React project!