Why data fetching differs in Next.js

Introduction

Next.js handles data fetching differently because it mixes server and client work to make websites faster and easier to build.

When you want your page to load faster by fetching data on the server before showing it.

When you need to update data on the client side after the page loads.

When you want to pre-build pages with data for better search engine results.

When you want to fetch data only when a user visits a page, not before.

When you want to combine server and client data fetching for a smooth experience.

Syntax

NextJS

export async function getServerSideProps(context) {
  // fetch data here
  const data = await fetchData();
  return { props: { data } };
}

export async function getStaticProps() {
  // fetch data here
  const data = await fetchData();
  return { props: { data } };
}

// Client-side fetching inside a React component
import { useEffect, useState } from 'react';

function Component() {
  const [data, setData] = useState(null);
  useEffect(() => {
    fetch('/api/data')
      .then(res => res.json())
      .then(setData);
  }, []);
  return <div>{data ? JSON.stringify(data) : 'Loading...'}</div>;
}

getServerSideProps runs on the server on every request.

getStaticProps runs at build time to create static pages.

Examples

This fetches data on the server every time someone visits the page.

NextJS

export async function getServerSideProps(context) {
  const res = await fetch('https://api.example.com/data');
  const data = await res.json();
  return { props: { data } };
}

This fetches data once when building the site, making the page very fast but data may be outdated.

NextJS

export async function getStaticProps() {
  const res = await fetch('https://api.example.com/data');
  const data = await res.json();
  return { props: { data } };
}

This fetches data on the client after the page loads, useful for user interactions.

NextJS

import { useEffect, useState } from 'react';

function Page() {
  const [data, setData] = useState(null);
  useEffect(() => {
    fetch('/api/data')
      .then(res => res.json())
      .then(setData);
  }, []);
  return <div>{data ? JSON.stringify(data) : 'Loading...'}</div>;
}

Sample Program

This example shows data fetched at build time for the post content, making the page fast to load. Comments are fetched on the client after the page loads, so users see the post immediately and comments appear shortly after.

NextJS

import { useState, useEffect } from 'react';

export async function getStaticProps() {
  const res = await fetch('https://jsonplaceholder.typicode.com/posts/1');
  const post = await res.json();
  return { props: { post } };
}

export default function PostPage({ post }) {
  const [comments, setComments] = useState(null);

  useEffect(() => {
    fetch('https://jsonplaceholder.typicode.com/posts/1/comments')
      .then(res => res.json())
      .then(setComments);
  }, []);

  return (
    <main>
      <h1>{post.title}</h1>
      <p>{post.body}</p>
      <section aria-label="Comments">
        <h2>Comments</h2>
        {comments ? (
          <ul>
            {comments.map(c => (
              <li key={c.id}>
                <strong>{c.name}:</strong> {c.body}
              </li>
            ))}
          </ul>
        ) : (
          <p>Loading comments...</p>
        )}
      </section>
    </main>
  );
}

Important Notes

Server-side fetching helps with SEO and fast first load.

Client-side fetching is good for data that changes often or depends on user actions.

Static generation is best for pages that don't change often.

Summary

Next.js uses different ways to fetch data depending on when and how you want it.

Server-side and static fetching happen before the page shows, client-side fetching happens after.

Choosing the right method helps your site load faster and work better for users.

Practice

1. Why does Next.js use different methods for data fetching?

easy

A. Because Next.js only works with static data

B. Because Next.js does not support client-side data fetching

C. Because all data must be fetched only on the server

D. Because data can be fetched at different times for better performance

Solution

1. Step 1: Understand data fetching timing in Next.js

   Next.js allows fetching data before the page loads (server-side or static) or after the page loads (client-side).

2. Step 2: Recognize the reason for multiple methods

   Using different methods helps improve performance and user experience by choosing the best time to fetch data.

3. Final Answer:

   Because data can be fetched at different times for better performance -> Option D

4. Quick Check:

   Data fetching timing = A [OK]

Hint: Think when data is needed: before or after page loads [OK]

Common Mistakes:

• Assuming Next.js only fetches data on the server
• Believing client-side fetching is not supported
• Thinking all data must be static

2. Which of the following is the correct way to fetch data at build time in Next.js?

easy

A. export async function getStaticProps() { return { props: {} } }

B. export async function getServerSideProps() { return { props: {} } }

C. export async function fetchData() { return { props: {} } }

D. export async function getClientSideProps() { return { props: {} } }

Solution

1. Step 1: Identify build-time data fetching method

   Next.js uses getStaticProps to fetch data at build time for static generation.

2. Step 2: Compare options with Next.js conventions

   getServerSideProps is for server-side rendering, not build time; others are invalid function names.

3. Final Answer:

   export async function getStaticProps() { return { props: {} } } -> Option A

4. Quick Check:

   Build-time fetch = getStaticProps A [OK]

Hint: Remember: Static = getStaticProps, Server = getServerSideProps [OK]

Common Mistakes:

• Confusing getServerSideProps with getStaticProps
• Using incorrect function names
• Thinking client-side fetching uses special props functions

3. What will be the rendered output if you use getServerSideProps to fetch data that changes every second?

medium

A. The page shows the data as it was at build time

B. The page never updates after first load

C. The page shows the latest data on every request

D. The page shows an error because data changes too fast

Solution

1. Step 1: Understand getServerSideProps behavior

   This function runs on every request, so it fetches fresh data each time the page loads.

2. Step 2: Apply to data changing every second

   Since data changes frequently, getServerSideProps ensures the page always shows the latest data.

3. Final Answer:

   The page shows the latest data on every request -> Option C

4. Quick Check:

   Server-side fetch = fresh data B [OK]

Hint: Server-side fetch updates on every request [OK]

Common Mistakes:

• Thinking getServerSideProps caches data at build time
• Assuming data never updates after first load
• Believing it causes errors with fast-changing data

4. Identify the error in this Next.js data fetching code:

export async function getStaticProps() {
  const res = await fetch('https://api.example.com/data')
  const data = await res.json()
  return { data }
}

medium

A. Missing return of props object wrapping data

B. fetch cannot be used inside getStaticProps

C. Async functions are not allowed in Next.js data fetching

D. The URL must be relative, not absolute

Solution

1. Step 1: Check return value format in getStaticProps

   Next.js expects an object with a props key containing the data, not just data alone.

2. Step 2: Identify the missing wrapper

   The code returns { data } but should return { props: { data } } for Next.js to pass props correctly.

3. Final Answer:

   Missing return of props object wrapping data -> Option A

4. Quick Check:

   Return props object = C [OK]

Hint: Always return { props: { ... } } in getStaticProps [OK]

Common Mistakes:

• Returning data directly without props wrapper
• Thinking fetch is disallowed in getStaticProps
• Believing async functions are forbidden

5. You want to show user-specific data that updates frequently but also want fast initial page load in Next.js. Which approach best fits this need?

hard

A. Use getStaticProps to fetch data and revalidate every second

B. Use getStaticProps for static data and fetch user data client-side after load

C. Fetch all data client-side only after page loads

D. Use getServerSideProps to fetch data on every request

Solution

1. Step 1: Analyze requirements for fast initial load and frequent updates

   Static data can be fetched at build time for fast load; user-specific data changes often and should be fetched client-side.

2. Step 2: Evaluate options

   Use getStaticProps to fetch data and revalidate every second revalidates too frequently and may cause performance issues; Use getServerSideProps to fetch data on every request delays initial load; Fetch all data client-side only after page loads delays all data; Use getStaticProps for static data and fetch user data client-side after load balances fast load and fresh user data.

3. Final Answer:

   Use getStaticProps for static data and fetch user data client-side after load -> Option B

4. Quick Check:

   Static + client fetch = D [OK]

Hint: Combine static build with client fetch for user data [OK]

Common Mistakes:

• Using only server-side fetching causing slow load
• Fetching everything client-side causing blank initial page
• Overusing revalidation causing unnecessary server load