Understanding "use client" in Next.js: What It Really Affects

Many developers misunderstand how "use client" works in Next.js App Router (React Server Components).

It doesn’t make everything below it client-rendered. It only changes the behavior of the file itself and what it directly imports.

1. The Common Misconception

You might have heard:

“If you use "use client", all your child components become client components.”

That’s false.

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2. The Real Rule

When you add "use client" at the top of a file:

• ✅ That file becomes a client component.
• ✅ Anything it imports becomes a client component too.
• 🚫 But components passed in as children props are not affected.

Children remain whatever they were defined as (server or client).

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3. Example: Safe Provider Pattern

// app/providers.tsx
"use client";

import { ThemeProvider } from "@mui/material";
import { QueryClientProvider } from "@tanstack/react-query";

export function Providers({ children }: { children: React.ReactNode }) {
  return (
    <ThemeProvider>
      <QueryClientProvider>{children}</QueryClientProvider>
    </ThemeProvider>
  );
}

This Providers component is a client component, because it needs React context, hooks, and browser logic.

But {children} are not converted to client components — they stay server-rendered.

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4. How It Works

When a server component (like your layout) calls a client component:

layout.tsx (server)
 └── Providers.tsx ("use client")
       └── children (server or client)

React Server Components serialize the child tree as HTML and pass it into the client boundary.

The Providers component doesn’t recompile or import the children — it just receives them as already-rendered markup.

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5. Why This Matters

Keeping most of your UI as server components gives you:

• Smaller JS bundles
• Faster page load
• Better SEO and streaming performance

Use "use client" only when you need:

• Hooks like useState, useEffect
• Event handlers (onClick, onChange)
• Access to window or browser APIs

So now I am no more "use client"-phobic. 😂