Why data fetching differs in Next.js - See It in Action

Understanding Why Data Fetching Differs in Next.js

📖 Scenario: You are building a simple blog homepage using Next.js. You want to show a list of posts fetched from an API. Next.js offers different ways to fetch data, and you want to understand how to set up data fetching correctly for server-side rendering and static generation.

🎯 Goal: Build a Next.js page that fetches blog post data using getStaticProps and displays the post titles. Learn why data fetching in Next.js differs from traditional React apps.

📋 What You'll Learn

Create a Next.js page component named BlogPage

Use getStaticProps to fetch data at build time

Display the list of post titles on the page

Understand the difference between server-side and client-side data fetching in Next.js

💡 Why This Matters

🌍 Real World

Next.js is used to build fast websites that load data before showing pages, improving user experience and search engine ranking.

💼 Career

Understanding Next.js data fetching methods is essential for frontend developers working with React frameworks to build scalable and SEO-friendly web apps.

1

Set up initial posts data array

Create a constant called posts that is an array of objects with these exact entries: { id: 1, title: 'Hello Next.js' } and { id: 2, title: 'Learn Data Fetching' }.

NextJS

# Your code here

Hint

Use const posts = [ ... ] with two objects inside the array.

2

Add getStaticProps function to fetch posts

Add an async function called getStaticProps that returns an object with a props key containing the posts array.

NextJS

const posts = [
  { id: 1, title: 'Hello Next.js' },
  { id: 2, title: 'Learn Data Fetching' }
];

// Your code here

Hint

Define getStaticProps as an async function that returns { props: { posts } }.

3

Create BlogPage component to display posts

Create a React functional component called BlogPage that accepts posts as a prop and returns a <ul> with each post's title inside a <li>. Use post.id as the key.

NextJS

const posts = [
  { id: 1, title: 'Hello Next.js' },
  { id: 2, title: 'Learn Data Fetching' }
];

export async function getStaticProps() {
  return {
    props: {
      posts
    }
  };
}

// Your code here

Hint

Use posts.map inside the component to create list items.

4

Export BlogPage as default and explain data fetching difference

Ensure BlogPage is exported as the default export. Understand that getStaticProps runs at build time on the server, so data fetching differs from client-side fetching in React by preloading data before the page loads.

NextJS

const posts = [
  { id: 1, title: 'Hello Next.js' },
  { id: 2, title: 'Learn Data Fetching' }
];

export async function getStaticProps() {
  return {
    props: {
      posts
    }
  };
}

export default function BlogPage({ posts }) {
  return (
    
      {posts.map(post => (
        {post.title}
      ))}
    
  );
}

// Your code here

Hint

Make sure BlogPage is the default export and getStaticProps is present.

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