Loading states for data in NextJS

Introduction

Loading states show users that data is being fetched. This helps avoid confusion and improves user experience.

When fetching data from an API to display on a page

When waiting for a server response after a user action

When loading content dynamically on scroll or navigation

When showing a placeholder while images or data load

Syntax

NextJS

import { useState, useEffect } from 'react';

function Component() {
  const [data, setData] = useState(null);
  const [loading, setLoading] = useState(true);

  useEffect(() => {
    fetch('/api/data')
      .then(res => res.json())
      .then(json => {
        setData(json);
        setLoading(false);
      });
  }, []);

  if (loading) return <p>Loading...</p>;
  return <div>{JSON.stringify(data)}</div>;
}

Use a loading state variable to track if data is still loading.

Show a simple message or spinner while loading is true.

Examples

Basic loading message shown while data is loading.

NextJS

const [loading, setLoading] = useState(true);

if (loading) {
  return <p>Loading data, please wait...</p>;
}

Fetch data and update loading state when done.

NextJS

useEffect(() => {
  fetch('/api/items')
    .then(res => res.json())
    .then(data => {
      setItems(data);
      setLoading(false);
    });
}, []);

Loading message with accessibility roles for screen readers.

NextJS

if (loading) {
  return <div role="status" aria-live="polite">Loading...</div>;
}

Sample Program

This component fetches a list of users from an API. While waiting, it shows "Loading users...". When data arrives, it shows the user names in a list.

NextJS

import { useState, useEffect } from 'react';

export default function UserList() {
  const [users, setUsers] = useState([]);
  const [loading, setLoading] = useState(true);

  useEffect(() => {
    async function fetchUsers() {
      const res = await fetch('https://jsonplaceholder.typicode.com/users');
      const data = await res.json();
      setUsers(data);
      setLoading(false);
    }
    fetchUsers();
  }, []);

  if (loading) {
    return <p>Loading users...</p>;
  }

  return (
    <ul>
      {users.map(user => (
        <li key={user.id}>{user.name}</li>
      ))}
    </ul>
  );
}

Important Notes

Always provide feedback to users when waiting for data.

Use semantic HTML and ARIA roles for accessibility.

Keep loading messages short and clear.

Summary

Loading states tell users data is coming.

Use a state variable to track loading.

Show a message or spinner while loading.

Practice

1. What is the main purpose of a loading state in a Next.js component?

easy

A. To speed up the data fetching process automatically

B. To show users that data is being fetched and the app is working

C. To permanently hide the data from users

D. To prevent users from clicking buttons

Solution

1. Step 1: Understand loading state purpose

   Loading states inform users that data is being fetched and the app is busy.

2. Step 2: Compare options

   Only To show users that data is being fetched and the app is working correctly describes this purpose; others are incorrect or unrelated.

3. Final Answer:

   To show users that data is being fetched and the app is working -> Option B

4. Quick Check:

   Loading state = user feedback [OK]

Hint: Loading states show progress to users [OK]

Common Mistakes:

• Thinking loading states speed up data fetching
• Confusing loading state with error state
• Ignoring user feedback during data fetch

2. Which of the following is the correct way to declare a loading state using React hooks in a Next.js component?

easy

A. const loading = useState(false);

B. let loading = true;

C. var loading = useState(true);

D. const [loading, setLoading] = useState(false);

Solution

1. Step 1: Identify correct useState syntax

   useState returns an array with state and setter, so destructuring is needed.

2. Step 2: Check options

   const [loading, setLoading] = useState(false); correctly uses array destructuring; others misuse useState or declare variables incorrectly.

3. Final Answer:

   const [loading, setLoading] = useState(false); -> Option D

4. Quick Check:

   useState syntax = destructuring [OK]

Hint: useState returns [state, setter], use array destructuring [OK]

Common Mistakes:

• Not destructuring useState result
• Using var or let instead of const
• Assigning useState directly to a variable

3. Given this Next.js component snippet, what will be rendered initially?

import { useState, useEffect } from 'react';

export default function DataLoader() {
  const [loading, setLoading] = useState(true);
  const [data, setData] = useState(null);

  useEffect(() => {
    setTimeout(() => {
      setData('Hello World');
      setLoading(false);
    }, 1000);
  }, []);

  if (loading) return <div>Loading...</div>;
  return <div>{data}</div>;
}

medium

A. Nothing renders

B. <div>Hello World</div>

C. <div>Loading...</div>

D. Error: data is null

Solution

1. Step 1: Check initial state values

   loading is true initially, so the component returns the loading message.

2. Step 2: Understand useEffect timing

   Data and loading update after 1 second, so initially only loading message shows.

3. Final Answer:

   <div>Loading...</div> -> Option C

4. Quick Check:

   Initial loading = true means show loading [OK]

Hint: Initial loading true means show loading message first [OK]

Common Mistakes:

• Assuming data shows immediately
• Ignoring initial loading state
• Expecting error when data is null

4. Identify the bug in this Next.js loading state code:

import { useState, useEffect } from 'react';

export default function Fetcher() {
  const [loading, setLoading] = useState(false);
  const [data, setData] = useState(null);

  useEffect(() => {
    setLoading(true);
    fetch('/api/data')
      .then(res => res.json())
      .then(json => {
        setData(json);
        setLoading(false);
      });
  }, []);

  if (loading) return <div>Loading...</div>;
  return <div>{JSON.stringify(data)}</div>;
}

medium

A. Initial loading state should be true, not false

B. Missing dependency array in useEffect

C. setLoading(true) should be after fetch

D. fetch call is missing await keyword

Solution

1. Step 1: Check initial loading state

   Loading starts false, but fetch begins immediately, so UI may skip loading message.

2. Step 2: Understand effect of initial loading false

   Because loading is false initially, component renders data area before fetch completes, showing null or empty.

3. Final Answer:

   Initial loading state should be true, not false -> Option A

4. Quick Check:

   Loading true initially shows loading UI correctly [OK]

Hint: Start loading as true to show loading UI immediately [OK]

Common Mistakes:

• Setting loading false initially hides loading UI
• Ignoring initial state impact on render
• Misplacing setLoading calls

5. You want to show a loading spinner while fetching data and then display the data or an error message if fetching fails. Which approach correctly handles loading, success, and error states in a Next.js component?

hard

A. Use three state variables: loading (boolean), data (object|null), error (string|null); update them accordingly during fetch lifecycle

B. Use only one state variable for data and show loading until data is not null

C. Use loading state only and ignore errors to simplify code

D. Fetch data outside component and pass as props to avoid loading states

Solution

1. Step 1: Identify states needed for full fetch lifecycle

   Loading, data, and error states cover all cases: waiting, success, and failure.

2. Step 2: Evaluate options

   Use three state variables: loading (boolean), data (object|null), error (string|null); update them accordingly during fetch lifecycle uses all three states properly; others miss error handling or loading feedback.

3. Final Answer:

   Use three state variables: loading (boolean), data (object|null), error (string|null); update them accordingly during fetch lifecycle -> Option A

4. Quick Check:

   Loading + data + error states = robust UI [OK]

Hint: Track loading, data, and error separately for clear UI states [OK]

Common Mistakes:

• Ignoring error state leads to silent failures
• Using only data state misses loading feedback
• Fetching data outside component loses dynamic loading UI