Why server components are the default in NextJS - Performance Evidence

Performance: Why server components are the default

HIGH IMPACT

This affects the initial page load speed and reduces client-side JavaScript execution, improving user experience.

Rendering UI components efficiently in Next.js

NextJS

export default async function Page() {
  const data = await fetchData();
  return <div>Data: {data.value}</div>;
}

This server component renders HTML on the server, sending minimal JS to the client and speeding up load.

📈 Performance GainSaves 50-100kb client bundle, reduces blocking time, improves LCP by 200-500ms

Rendering UI components efficiently in Next.js

NextJS

'use client'

import React from 'react';

export default function Page() {
  const [count, setCount] = React.useState(0);
  return <button onClick={() => setCount(count + 1)}>Count: {count}</button>;
}

This client component sends all React code to the browser, increasing bundle size and delaying initial paint.

📉 Performance CostAdds 50-100kb to client bundle, blocking rendering until JS loads and executes

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
Client Components by default	More DOM nodes from hydration	Multiple reflows during hydration	Higher paint cost due to JS execution	[X] Bad
Server Components by default	Minimal DOM nodes, static HTML	Single reflow on initial load	Lower paint cost, faster display	[OK] Good

Rendering Pipeline

Server components render HTML on the server, so the browser receives ready-to-display content without waiting for JS to load. This reduces work in Style Calculation, Layout, and Paint stages on the client.

→HTML Parsing

→Style Calculation

→Layout

→Paint

⚠️ BottleneckClient-side JavaScript execution and hydration

Core Web Vital Affected

LCP

This affects the initial page load speed and reduces client-side JavaScript execution, improving user experience.

Optimization Tips

1Use server components to reduce client JavaScript bundle size.

2Server components speed up initial content display by sending pre-rendered HTML.

3Avoid unnecessary client components to minimize hydration and reflow costs.

Performance Quiz - 3 Questions

Why do server components improve Largest Contentful Paint (LCP) in Next.js?

A They send pre-rendered HTML to the browser, reducing client JS work.

B They increase client-side JavaScript bundle size.

C They delay rendering until all client scripts load.

D They require more reflows during hydration.

DevTools: Performance

How to check: Record page load and look for scripting time and time to first meaningful paint.

What to look for: Lower scripting time and faster Largest Contentful Paint indicate good server component usage.

Practice

1. Why are server components the default in Next.js?

easy

A. They allow direct access to browser events and state management.

B. They improve speed by running on the server and sending only HTML to the browser.

C. They require less server resources by running on the client.

D. They enable real-time updates without refreshing the page.

Solution

1. Step 1: Understand server component behavior

   Server components run on the server and send only HTML to the browser, reducing data transfer and improving speed.

2. Step 2: Compare with client components

   Client components handle browser events and state, but server components focus on fast, secure rendering.

3. Final Answer:

   They improve speed by running on the server and sending only HTML to the browser. -> Option B

4. Quick Check:

   Server components = faster, secure HTML delivery [OK]

Hint: Server components send HTML, client components handle events [OK]

Common Mistakes:

• Confusing server components with client-side event handling
• Thinking server components run in the browser
• Assuming server components manage state like client components

2. Which of the following is the correct way to mark a component as a client component in Next.js?

easy

A. Use export default clientComponent() syntax.

B. Wrap the component in <ClientComponent> tags.

C. Add the directive use client at the top of the file.

D. Add client: true in the component props.

Solution

1. Step 1: Recall client component syntax

   In Next.js, to mark a component as client-side, you add the directive use client at the very top of the file.

2. Step 2: Eliminate incorrect options

   Wrapping in tags, special export syntax, or props flags are not valid ways to mark client components.

3. Final Answer:

   Add the directive use client at the top of the file. -> Option C

4. Quick Check:

   Client component directive = 'use client' [OK]

Hint: Client components start with 'use client' directive [OK]

Common Mistakes:

• Trying to mark client components with props or wrappers
• Placing 'use client' inside the component body
• Confusing export syntax with client directives

3. Consider this Next.js component code:

export default function Page() {
  return (
    <div>Hello from server component</div>
  )
}

What will the browser receive when this page loads?

medium

A. Plain HTML content: <div>Hello from server component</div>.

B. An error because no client directive is present.

C. A fully interactive React component with event handlers.

D. Empty content because server components do not render.

Solution

1. Step 1: Identify component type

   The component has no 'use client' directive, so it is a server component by default.

2. Step 2: Understand server component output

   Server components render HTML on the server and send plain HTML to the browser without React event handlers.

3. Final Answer:

   Plain HTML content: <div>Hello from server component</div>. -> Option A

4. Quick Check:

   Server component output = plain HTML [OK]

Hint: No 'use client' means server component sends HTML only [OK]

Common Mistakes:

• Expecting React interactivity without 'use client'
• Thinking server components cause errors without client directive
• Assuming server components send JavaScript to browser

4. You have this Next.js component:

export default function Button() {
  const [count, setCount] = React.useState(0);
  return <button onClick={() => setCount(count + 1)}>Clicked {count} times</button>;
}

What is the main problem with this code in Next.js 13+?

medium

A. Buttons cannot have event handlers in Next.js.

B. The useState hook is not imported from React.

C. The arrow function in onClick is invalid syntax.

D. It lacks the use client directive, so state and events won't work.

Solution

1. Step 1: Check component type and hooks usage

   The component uses React state and event handlers, which require client-side execution.

2. Step 2: Identify missing client directive

   Without the 'use client' directive at the top, this component is treated as a server component, so hooks and events won't work.

3. Final Answer:

   It lacks the use client directive, so state and events won't work. -> Option D

4. Quick Check:

   State + events need 'use client' directive [OK]

Hint: State or events require 'use client' directive [OK]

Common Mistakes:

• Forgetting to add 'use client' for interactive components
• Assuming hooks work in server components
• Thinking arrow functions cause syntax errors here

5. You want to build a Next.js page that fetches data securely on the server and shows a button that increments a counter on click. How should you organize your components?

hard

A. Use a server component for data fetching and embed a client component for the button with state.

B. Make the entire page a client component to handle data fetching and button state.

C. Use only server components because client components are slower.

D. Fetch data in the client component and handle button state in the server component.

Solution

1. Step 1: Separate concerns by component type

   Data fetching is best done in server components for security and speed, while interactive UI needs client components.

2. Step 2: Combine server and client components properly

   Use a server component to fetch and render data, then include a client component inside it for the button with state and events.

3. Final Answer:

   Use a server component for data fetching and embed a client component for the button with state. -> Option A

4. Quick Check:

   Server fetch + client interactivity = best practice [OK]

Hint: Fetch on server, interactive parts on client [OK]

Common Mistakes:

• Making entire page client-side losing server benefits
• Trying to fetch data inside client components
• Mixing state logic in server components