Async server components in NextJS - Mini Project: Build & Apply

Async Server Components in Next.js

📖 Scenario: You are building a simple Next.js app that fetches user data from an API and displays it on the server side. This helps your app load faster and improves SEO.

🎯 Goal: Create an async server component in Next.js that fetches user data from a public API and renders the user names in a list.

📋 What You'll Learn

Create a server component that fetches data asynchronously

Use the fetch API inside the server component

Render the fetched data as a list of user names

Use Next.js 14+ App Router conventions

💡 Why This Matters

🌍 Real World

Fetching data on the server before rendering pages is common in real-world web apps to improve speed and SEO.

💼 Career

Understanding async server components is essential for modern Next.js development roles focused on performance and user experience.

1

Create the basic server component

Create a file called page.tsx inside the app directory. Inside it, create a default exported async function called Page that returns a simple <div>Loading users...</div> JSX element.

NextJS

export default async function Page() {
  // Your code here
}

Hint

This is the basic structure of a server component in Next.js. It must be an async function to fetch data later.

2

Add the API URL configuration

Inside page.tsx, add a constant called apiUrl and set it to the string "https://jsonplaceholder.typicode.com/users". This will be the URL to fetch user data.

NextJS

const apiUrl = "https://jsonplaceholder.typicode.com/users";

export default async function Page() {
  return Loading users...;
  // Your code here
}

Hint

This URL will be used to fetch user data in the next step.

3

Fetch user data asynchronously

Inside the Page function, use await fetch(apiUrl) to get the response. Then use await response.json() to parse the JSON data and store it in a variable called users.

NextJS

const apiUrl = "https://jsonplaceholder.typicode.com/users";

export default async function Page() {
  // Your code here
}

Hint

Use await to wait for the fetch and JSON parsing to complete before continuing.

4

Render the list of user names

Replace the <div>Loading users...</div> with a <ul> element. Inside it, use users.map to create a <li> for each user showing their name. Make sure each <li> has a unique key using the user's id.

NextJS

const apiUrl = "https://jsonplaceholder.typicode.com/users";

export default async function Page() {
  const response = await fetch(apiUrl);
  const users = await response.json();
  // Your code here
}

Hint

Use JSX to loop over the users and display their names in a list.

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