React is evolving — fast. With the introduction of Server Components in React 18+ and the rise of frameworks like Next.js 13+, developers are now writing apps that seamlessly mix client-side interactivity with server-rendered performance.
At the centre of this transformation are two simple but powerful directives:
- ‘use client’
- ‘use server’
While they might look like minor syntax additions, they’re fundamentally changing how React applications are structured and shipped, especially in server-first frameworks.
In this blog, we’ll explore what these directives mean, when to use them, and how modern teams — including those that hire ReactJS developers — are leveraging them to build more efficient, scalable web apps.
What are ‘use client’ and ‘use server’?
These directives are string literals placed at the top of your file, used to explicitly tell the React compiler where a component or module should execute.
‘use client’
Marks a component as a Client Component — meaning it will be rendered and hydrated in the browser. It supports interactivity, browser APIs, and hooks like useState, useEffect, etc.
‘use server’
Marks a function as a Server Action or Server Component — meaning it runs only on the server, without shipping any code to the client.
This distinction brings a clean separation between interactive and static code, giving React JS development company teams more control over performance and security.
Why These Directives Matter in Modern React Architecture
Traditionally, everything in React was rendered to the client unless you specifically used SSR (Server-Side Rendering). Now, thanks to Server Components and React’s evolving rendering model, we can:
- Ship less JavaScript to the browser
- Run data fetching and heavy logic on the server.
- Keep client bundles small and fast.
- Use React Server Actions for mutations without client APIs
This unlocks true hybrid rendering, allowing developers and companies offering ReactJS development services to design apps that scale better, load faster, and perform reliably.
When to Use ‘use client’ — And When Not To
Use ‘use client’ when:
- Your component uses state or side effects (useState, useEffect)
- You need interactivity (forms, modals, drag-and-drop)
- You’re accessing browser-only APIs (e.g., localStorage, navigator, or DOM)
Avoid ‘use client’ if:
- The component doesn’t need interactivity
- It only renders static data or markup.
- You can push the logic to the server for faster load time.
Reducing ‘use client’ components can dramatically reduce your JS bundle size — a key metric for any ReactJS web development company building apps for performance-focused clients.
Understanding ‘use server’: Not Just for Components
Unlike ‘use client’, which applies to all components, ‘use server’ is mostly used in server actions or data-fetching functions.
This allows you to:
- Handle form submissions without API routes
- Perform database writes securely.
- Keep logic on the server, reducing client-side exposure.
For example, instead of using fetch(‘/api/submit’), you can write
js
CopyEdit
‘use server’;
export async function submitForm(data) {
// Save to database directly
}
When integrated properly, this leads to cleaner APIs, fewer client-server round trips, and better security — all of which modern React JS development company teams are actively implementing in production apps.
Best Practices for Using These Directives
To make the most of ‘use client’ and ‘use server’, follow these patterns:
1. Start Server-First, Add Interactivity Later
By default, build components as Server Components. Add ‘use client’ only when needed. This keeps your app lean by default.
2. Keep Boundaries Clear
Avoid mixing logic between client and server files. Server components can import server-only modules like fs, crypto, or database clients, but client components cannot.
3. Memoize and Split
Use React.memo and code-splitting techniques in client components to optimise performance further. Pair with Suspense where needed.
4. Group Client Components
Instead of marking every interactive component separately, group related ones under a single ‘use client’ wrapper if they’re part of the same UI unit.
This is something skilled teams that hire ReactJS developers often do to optimise hydration and reduce the JS payload.
Common Pitfalls to Avoid
While powerful, this new rendering model introduces new challenges:
- Hydration mismatches between server and client can occur if the state is incorrectly shared
- Importing client-only libraries into server components can throw runtime errors.
- Misplacing ‘use client’ can accidentally bloat server bundles.
This is why businesses often consult a ReactJS development company when adopting the new architecture — to ensure clean separation and performance gains.
How Frameworks Like Next.js Use These Directives
Next.js 13+ and 14 have deeply integrated ‘use client’ and ‘use server’ into their app directory model. It allows:
- Fine-grained control over what gets rendered where
- Automatic streaming and partial hydration
- Built-in routing and server action support
As of 2025, most advanced ReactJS web development company teams have adopted the Next.js app router architecture, making full use of these directives for maintainable, high-performance codebases.
When Should You Adopt ‘use client’ and ‘use server’?
Adoption is a must if:
- You’re starting a new React or Next.js project
- You’re working on a performance-critical app.
- You want better control over bundle size and hydration.
- You’re integrating server-side logic directly into React components.
Even for legacy apps, you can incrementally adopt this model by converting specific parts of your app, especially components that don’t need to be interactive.
Conclusion: Build Smarter, Faster React Apps in 2025
React’s ‘use client’ and ‘use server’ directives may be small additions, but they represent a massive shift in how modern React applications are built.
By clearly separating interactivity from rendering logic, they allow you to ship faster apps, reduce bundle sizes, and simplify server-client communication — all while improving the developer experience.
Whether you’re modernising an existing React stack or launching a new product, working with a future-focused ReactJS development company or choosing to hire ReactJS developers skilled in this hybrid model will give you a significant head start.