Everything You Need to Know About React Server Components in React 19
React 19 has arrived, bringing exciting new features and improvements that streamline development. What sets this release apart is React's significant shift toward server-side capabilities, marking a new chapter in how we build applications.
In this blog post, I’ll dive into these groundbreaking server-side features and demonstrate their potential by relying on a meta-framework. Specifically, I’ll attempt to build things using Next.js, exploring how React 19 can empower developers to innovate beyond traditional approaches.
By the end, I’ll share my experience, insights, and whether I believe React 19’s server-first features live up to the hype
Quick Primer on Server-Side Rendering (SSR)
Server-Side Rendering (SSR) is a technique where a web application's HTML is generated on the server rather than in the browser. With Server-Side Rendering (SSR), the initial render occurs on the server, producing a complete HTML page that is sent to the browser, similar to how a "traditional" backend would render a page. Once the browser receives this HTML, a process called hydration begins. During hydration, React binds event listeners, initializes the state, and enhances the static HTML into a fully interactive React app.
After hydration, all subsequent updates (e.g., due to state changes) are handled entirely on the client side, functioning just like a regular Single Page Application (SPA). However, because only the initial render is performed server-side, the full JavaScript bundle must still be sent to the client to enable interactivity and manage further updates.
What are React Server Components?
Server Components are a new type of Component that renders ahead of time, before bundling, in an environment separate from your client app or SSR server. React Server Components (RSC) work differently from traditional Server-Side Rendering (SSR). Instead of sending plain HTML to the client, the backend sends serialized objects that describe the rendered components.
On the client, these objects are used to create DOM nodes, but there’s no hydration involved because the actual rendering always happens on the server. This means the source code of server-rendered components stays on the backend and is never sent to the client, keeping the client-side simpler and more secure.
Here's a quick example of a “Server Component”:
// ExampleServerComponent.server.jsx
// This component fetches data on the server and renders the result.
// The client never sees the component’s source code or data fetching logic.
import React from 'react';
async function ExampleServerComponent() {
// Perform server-side data fetching here
const data = await fetch('https://api.example.com/posts').then(res => res.json());
return (
<ul>
{data.map(post => (
<li key={post.id}>{post.title}</li>
))}
</ul>
);
}
export default ExampleServerComponent;
Wait, what's happening here? “Function components can't be asynchronous right?” Normally, yes—on the client side, that’s the case. But on the server, React treats components differently. Here, server components can be asynchronous. They can wait for data to load and perform other async operations before producing their final rendered output.
Once the server has computed this output, it sends a static representation of the UI to the client. There’s no additional hydration or updating needed, because from React’s point of view, the server component’s job is done. The client receives a finished snapshot of the UI that never re-renders, leaving the interactive logic to other parts of the app.
React Server Functions
React Server Functions are functions that run on the server at build time or request time, allowing you to fetch data and render initial HTML before it reaches the client’s browser. This approach improves performance and user experience by offloading data fetching and heavy computation from the client-side JavaScript bundle to the server.
// app/EmptyNote.jsx (Server Component)
import Button from './Button'; // Assume Button is a Client Component
import db from '../lib/db'; // Assume db is a database client
export default function EmptyNote() {
// A Server Action to create a new note in the database
async function createNoteAction() {
'use server';
await db.notes.create({ text: 'My new note' });
}
// The Button component is a Client Component that, when clicked,
// invokes the server action and triggers database mutation on the server.
return (
<div>
<h1>Create a New Note</h1>
<Button onClick={createNoteAction}>Create Note</Button>
</div>
);
}
- The EmptyNote component is a Server Component, which means it primarily runs on the server. Inside it, we define a server function named createNoteAction that is marked with 'use server'. This tells the React runtime that this function should only run on the server.
- When a user clicks the Button, the createNoteAction server function is invoked from the client, causing the server to run the associated logic (in this case, creating a new note in the database).
- Because the heavy lifting (database interaction) happens on the server, the client doesn’t need to manage thesdetails, improving efficiency and reducing complexity on the client side.
Key Benefits of React Server Components
- Asynchronous Logic on the Server: Since Server Components run on the backend, it’s perfectly fine for them to use async/await to fetch data or perform operations before rendering. This leads to cleaner, more direct data-fetching patterns without client-side complexity.
- No Client Bundling: The component’s code and logic remain on the server, meaning the browser only receives a serialised representation of the rendered result.
- Improved Performance & Security: Since no component code is shipped to the client, bundle sizes are reduced, and sensitive logic stays hidden on the server
Challenges and Limitations
The key thing to understand is this: Server Components never re-render. They run once on the server to generate the UI. The rendered value is sent to the client and locked in place. As far as React is concerned, this output is immutable, and will never change
This means that a big chunk of React's API is incompatible with Server Components.
- We need to put side effects inside a useEffect callback
- Event listeners like onClick cannot be used directly in Server Components since these are static by design.
Is RSC the new SSR?
It might create confusion that it is the new version of the SSR, something like SSR 2.0, but it’s not.
Let’s clear up this misunderstanding, React SC are not SSR version 2.0. Instead, imagine them like distinct ingredients that, when combined, cook up a perfectly balanced dish.
We still rely on the SSR to generate the initial HTML as we discussed before. RSC builds on top of that , removing certain components like client side JS bundle, ensuring the servers output is final.
Conclusion and Future Outlook
Finally you can get started with React server components using meta frameworks like Next's , Remix and others as mentioned in their <a href="http://https://react.dev/learn/start-a-new-react-project "documents"" target="_blank">documents.
We began with a world where the server handled most of the heavy lifting, delivering simple HTML directly to the client. Then came the era when we moved logic into the browser to enable richer, more interactive interfaces. Today, technologies like React Server Components bring these two approaches together, letting us offload data fetching and initial rendering to the server without sacrificing the dynamic, responsive experiences made possible by client-side frameworks. Instead of forcing a choice between the simplicity of server-side architectures or the flexibility of client-side logic, we now have a balanced model that blends the best of both worlds. This means lighter client bundles, faster initial loads, and more maintainable code—all without giving up the nuanced interactions and engaging UIs we’ve come to expect.
