Async server components in NextJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define an async server component in Next.js.

NextJS

export default async function [1]() {
  return <div>Hello from server component</div>;
}

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

AComponent

BServer

CApp

DPage

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-standard function name that Next.js does not recognize.

The default export function name is often Page in Next.js server components.

2fill in blank

medium

Complete the code to fetch data inside an async server component.

NextJS

export default async function Page() {
  const res = await fetch('[1]');
  const data = await res.json();
  return <div>{data.message}</div>;
}

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

A/api/message

Bhttps://example.com/api

C/api/data

Dhttp://localhost/api

Attempts:

3 left

💡 Hint

Common Mistakes

Using an absolute URL when a relative API route is expected.

Using /api/message is a common local API route in Next.js for fetching data.

3fill in blank

hard

Fix the error in the async server component by completing the code.

NextJS

export default [1] function Page() {
  const data = await fetch('/api/info').then(res => res.json());
  return <div>{data.info}</div>;
}

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

Aawait

Basync

Casync function

Dfunction async

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to mark the function as async causes syntax errors.

The component function must be marked async to use await inside it.

4fill in blank

hard

Fill both blanks to correctly fetch and display data in an async server component.

NextJS

export default async function Page() {
  const res = await fetch('[1]');
  const data = await res.[2]();
  return <div>{data.title}</div>;
}

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

A/api/posts

Bjson

Ctext

D/api/users

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong API route or parsing method causes errors or wrong output.

Use /api/posts as the fetch URL and json() to parse the response.

5fill in blank

hard

Fill all three blanks to create an async server component that fetches and renders a list.

NextJS

export default async function Page() {
  const res = await fetch('[1]');
  const posts = await res.[2]();
  return (
    <ul>
      {posts.[3](post => <li key={post.id}>{post.title}</li>)}
    </ul>
  );
}

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

A/api/posts

Bjson

Cmap

D/api/comments

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong fetch URL, parsing method, or forgetting to map over the array.

The component fetches from /api/posts, parses JSON, and maps over posts to render list items.

Practice

1. What is the main benefit of using async server components in Next.js?

easy

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

B. They allow client-side state management inside the component.

C. They automatically cache data on the client device.

D. They fetch data before rendering, sending ready HTML to the browser.

Solution

1. Step 1: Understand async server components purpose

   Async server components fetch data on the server before rendering the page.

2. Step 2: Identify the benefit of pre-fetching data

   This means the browser receives fully rendered HTML, improving speed and user experience.

3. Final Answer:

   They fetch data before rendering, sending ready HTML to the browser. -> Option D

4. Quick Check:

   Async server components = fetch data first [OK]

Hint: Async server components fetch data before rendering [OK]

Common Mistakes:

• Thinking async components run on the client
• Confusing caching with async data fetching
• Assuming real-time updates happen automatically

2. Which of the following is the correct way to define an async server component in Next.js?

easy

A. async function MyComponent() { const data = await fetchData(); return {data}; }

B. function MyComponent() { const data = await fetchData(); return {data}; }

C. const MyComponent = () => { const data = await fetchData(); return {data}; }

D. const MyComponent = async () => { fetchData().then(data => {data}); }

Solution

1. Step 1: Identify async function syntax for components

   Next.js requires the component function to be marked async to use await inside.

2. Step 2: Check each option for correct async usage

   async function MyComponent() { const data = await fetchData(); return
   {data}; } correctly defines an async function and uses await inside. function MyComponent() { const data = await fetchData(); return

   {data}

   ; } misses async keyword. const MyComponent = () => { const data = await fetchData(); return

   {data}

   ; } uses arrow function but misses async. const MyComponent = async () => { fetchData().then(data =>

   {data}

   ); } uses then() but does not return JSX properly.

3. Final Answer:

   async function MyComponent() { const data = await fetchData(); return <div>{data}</div>; } -> Option A

4. Quick Check:

   Async keyword + await inside = async function MyComponent() { const data = await fetchData(); return
   {data}
   ; } [OK]

Hint: Async components must be declared with async keyword [OK]

Common Mistakes:

• Forgetting to add async keyword
• Using await without async function
• Returning JSX inside then() without return statement

3. Given this async server component code, what will be rendered?

async function Greeting() {
  const name = await Promise.resolve('Alice');
  return <h1>Hello, {name}!</h1>;
}

medium

A. <h1>Hello, Alice!</h1>

B. Hello, {name}!

C. Promise { 'Alice' }

D. Error: Cannot use await here

Solution

1. Step 1: Understand async function behavior in server components

   The function awaits the resolved promise 'Alice' and stores it in name.

2. Step 2: Render JSX with awaited value

   The component returns an h1 element with the text 'Hello, Alice!'. This HTML is sent to the browser.

3. Final Answer:

   <h1>Hello, Alice!</h1> -> Option A

4. Quick Check:

   Await resolves promise, renders value [OK]

Hint: Await resolves promise before rendering JSX [OK]

Common Mistakes:

• Thinking JSX shows variable name literally
• Expecting promise object to render
• Assuming await is disallowed in server components

4. What is wrong with this async server component code?

async function UserProfile() {
  const user = fetch('/api/user');
  return <div>{user.name}</div>;
}

medium

A. Cannot use fetch inside server components.

B. Missing await before fetch call, so user is a promise, not data.

C. JSX cannot contain expressions like {user.name}.

D. Function should not be async if it returns JSX.

Solution

1. Step 1: Check fetch usage in async function

   fetch returns a promise, so it must be awaited to get the data.

2. Step 2: Identify the error in accessing user.name

   Without await, user is a promise object, so user.name is undefined causing error.

3. Final Answer:

   Missing await before fetch call, so user is a promise, not data. -> Option B

4. Quick Check:

   Always await fetch to get data [OK]

Hint: Always await fetch to get resolved data [OK]

Common Mistakes:

• Forgetting await before fetch
• Thinking fetch is disallowed in server components
• Misunderstanding JSX expressions

5. You want to fetch user data and posts in an async server component and render them together. Which code correctly fetches both before rendering?

async function Dashboard() {
  const user = await fetch('/api/user').then(res => res.json());
  const posts = fetch('/api/posts').then(res => res.json());
  return (
    <div>
      <h1>{user.name}</h1>
      <ul>{posts.map(post => <li key={post.id}>{post.title}</li>)}

hard

A. Use then() only without await for both fetches.

B. Remove await before fetch('/api/user') to run both fetches in parallel.

C. Add await before fetch('/api/posts') to wait for posts data.

D. Return JSX before fetching posts to speed up rendering.

Solution

1. Step 1: Identify missing await for posts fetch

   The posts fetch is missing await, so posts is a promise, not data.

2. Step 2: Fix by adding await to posts fetch

   Adding await ensures posts data is ready before rendering the list.

3. Final Answer:

   Add await before fetch('/api/posts') to wait for posts data. -> Option C

4. Quick Check:

   Await all fetches before rendering [OK]

Hint: Await all fetches before using their data [OK]

Common Mistakes:

• Forgetting await on second fetch
• Removing await on first fetch causing errors
• Returning JSX before data is ready