Loading states for data in NextJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the React hook used for managing state.

NextJS

import React, { [1] } from 'react';

Drag options to blanks, or click blank then click option'

AuseState

BuseEffect

CuseContext

DuseRef

Attempts:

3 left

💡 Hint

Common Mistakes

Using useEffect instead of useState for state management.

Forgetting to import the hook from React.

The useState hook is used to manage state in functional components, which is essential for handling loading states.

2fill in blank

medium

Complete the code to fetch data inside a React effect hook.

NextJS

useEffect(() => {
  fetch('/api/data')
    .then(response => response.json())
    .then(data => setData(data))
    .finally(() => set[1](false));
}, []);

Drag options to blanks, or click blank then click option'

ALoad

BisLoading

Cloading

DLoading

Attempts:

3 left

💡 Hint

Common Mistakes

Using uppercase variable names which are not valid for state variables.

Confusing the loading variable name with other similar names.

The state variable for loading is usually named loading in camelCase. The setter function is setLoading, so here we call setLoading(false) to indicate loading is done.

3fill in blank

hard

Fix the error in the conditional rendering to show loading text.

NextJS

if ([1]) {
  return <p>Loading...</p>;
}

Drag options to blanks, or click blank then click option'

AsetLoading

Bdata

Cloading

DisLoading

Attempts:

3 left

💡 Hint

Common Mistakes

Using the setter function setLoading instead of the state variable.

Checking the data variable instead of loading state.

The variable loading holds the boolean state for loading. We check it to decide whether to show the loading message. setLoading is a function and cannot be used here.

4fill in blank

hard

Fill both blanks to initialize loading state and data state using React hooks.

NextJS

const [[1], setLoading] = useState(true);
const [[2], setData] = useState(null);

Drag options to blanks, or click blank then click option'

Aloading

Bdata

CisLoading

Ditems

Attempts:

3 left

💡 Hint

Common Mistakes

Using inconsistent variable names that don't match setter functions.

Initializing loading state as false instead of true.

We initialize loading state as true because data is loading initially. The data state is named data and starts as null.

5fill in blank

hard

Fill all three blanks to render data or loading message conditionally.

NextJS

return (
  <main>
    { [1] ? (
      <p>Loading...</p>
    ) : (
      <ul>
        { [2]?.map(item => (
          <li key={item.id}>[3]</li>
        ))}
      </ul>
    )}
  </main>
);

Drag options to blanks, or click blank then click option'

Aloading

Bdata

Citem.name

Ditems

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong variable names for loading or data.

Trying to map over a variable that is not an array.

Not accessing the correct property of the item.

We check loading to show the loading message. When not loading, we map over data to render each item.name inside list items.

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