Fetching APIs in frontmatter in Astro - Mini Project: Build & Apply

Fetching APIs in frontmatter

📖 Scenario: You are building a simple Astro website that shows a list of users fetched from an external API. You want to load this data in the frontmatter of your Astro component so it is ready when the page renders.

🎯 Goal: Create an Astro component that fetches user data from a public API in the frontmatter and displays the users' names in a list on the page.

📋 What You'll Learn

Use Astro frontmatter to fetch data from the API

Store the fetched data in a variable called users

Render a list of user names inside a <ul> element

Use semantic HTML and accessible markup

💡 Why This Matters

🌍 Real World

Fetching data from APIs in frontmatter is common in Astro to prepare data before rendering pages, improving performance and SEO.

💼 Career

Understanding how to fetch and use API data in Astro components is essential for frontend developers working with modern static site generators and frameworks.

1

Set up the Astro frontmatter and fetch data

In the frontmatter of your Astro component, write an async function called fetchUsers that fetches data from https://jsonplaceholder.typicode.com/users. Then create a constant called users that awaits the JSON response by calling fetchUsers().

Astro

---
// Your code here to define fetchUsers and users
---

Hint

Use fetch inside an async function and then call it with await to get the JSON data.

2

Add a title variable for the page

Add a constant variable called pageTitle in the frontmatter and set it to the string 'User List'.

Astro

---
async function fetchUsers() {
  const response = await fetch('https://jsonplaceholder.typicode.com/users');
  return await response.json();
}

const users = await fetchUsers();

// Your code here to add pageTitle
---

Hint

Just create a constant pageTitle and assign the string 'User List'.

3

Render the page title and user names list

Below the frontmatter, write HTML that renders an <h1> element showing the pageTitle. Then create an unordered list <ul> that uses a {users.map((user) => ...)} expression to render each user's name inside a <li> element.

Astro

---
async function fetchUsers() {
  const response = await fetch('https://jsonplaceholder.typicode.com/users');
  return await response.json();
}

const users = await fetchUsers();
const pageTitle = 'User List';
---

Hint

Use curly braces {} to embed JavaScript expressions in Astro HTML. Use users.map to loop over the array.

4

Add semantic HTML and accessibility features

Wrap the content inside a <main> element. Add an aria-label attribute with the value 'User list section' to the <ul> element for accessibility.

Astro

---
async function fetchUsers() {
  const response = await fetch('https://jsonplaceholder.typicode.com/users');
  return await response.json();
}

const users = await fetchUsers();
const pageTitle = 'User List';
---

 and add aria-label to  -->

Hint

Use semantic <main> to wrap the page content and add aria-label to the list for screen readers.

Practice

1. What is the main purpose of fetching APIs in the frontmatter of an Astro component?

easy

A. To get data before the page renders so it shows fresh content immediately

B. To delay data loading until after the page is fully loaded

C. To style the page using CSS variables

D. To handle user input events on the page

Solution

1. Step 1: Understand frontmatter role in Astro

   Frontmatter runs before the page renders, allowing data fetching early.

2. Step 2: Purpose of fetching API in frontmatter

   Fetching data here ensures the page shows fresh content immediately when loaded.

3. Final Answer:

   To get data before the page renders so it shows fresh content immediately -> Option A

4. Quick Check:

   Fetching in frontmatter = fresh data before render [OK]

Hint: Frontmatter fetches data before page shows [OK]

Common Mistakes:

• Thinking data loads after page renders
• Confusing frontmatter with styling or events
• Assuming frontmatter runs on client side

2. Which of the following is the correct syntax to fetch data in Astro frontmatter?

easy

A. ---
const response = await fetch('https://api.example.com/data');
const data = await response.json();
---

B.

C. const data = fetch('https://api.example.com/data');

D. ---
fetch('https://api.example.com/data')
---

Solution

1. Step 1: Identify frontmatter syntax

   Astro frontmatter uses triple dashes --- to enclose code that runs before rendering.

2. Step 2: Correct async fetch usage

   Using await fetch and await response.json() inside frontmatter is correct to get JSON data.

3. Final Answer:

   --- const response = await fetch('https://api.example.com/data'); const data = await response.json(); --- -> Option A

4. Quick Check:

   Frontmatter uses --- and await fetch [OK]

Hint: Use --- and await fetch inside frontmatter [OK]

Common Mistakes:

• Using fetch without await in frontmatter
• Placing fetch inside <script> tag instead of frontmatter
• Not parsing response with .json()

3. Given this Astro frontmatter code, what will be the value of data.message in the component?

---
const response = await fetch('https://api.example.com/greet');
const data = await response.json();
---

{data.message}

Assuming the API returns JSON: { "message": "Hello, Astro!" }

medium

A. undefined

B. "Hello, Astro!"

C. SyntaxError

D. null

Solution

1. Step 1: Understand fetch and JSON parsing

   The fetch gets the API response, and await response.json() parses it into an object with a message property.

2. Step 2: Accessing data.message in component

   The component uses {data.message} which will display the string from the API: "Hello, Astro!".

3. Final Answer:

   "Hello, Astro!" -> Option B

4. Quick Check:

   API message property = "Hello, Astro!" [OK]

Hint: Parsed JSON data shows in component as expected [OK]

Common Mistakes:

• Forgetting to await response.json()
• Trying to access data before fetch completes
• Assuming data.message is undefined or null

4. What is wrong with this Astro frontmatter code?

---
const data = fetch('https://api.example.com/data');
const json = data.json();
---

medium

A. Using triple dashes --- incorrectly

B. json() is not a function

C. fetch URL is invalid syntax

D. Missing await before fetch and json() calls

Solution

1. Step 1: Check async fetch usage

   fetch returns a Promise, so it must be awaited to get the response object.

2. Step 2: Check json() call

   response.json() also returns a Promise and must be awaited to get parsed data.

3. Final Answer:

   Missing await before fetch and json() calls -> Option D

4. Quick Check:

   Always await fetch and response.json() [OK]

Hint: Always await fetch and json() in frontmatter [OK]

Common Mistakes:

• Not using await causing unresolved Promises
• Assuming fetch is synchronous
• Calling json() on Promise instead of response

5. You want to fetch a list of users from an API in Astro frontmatter and display their names. Which approach correctly fetches and prepares the data for rendering?

---
// Option A
const res = await fetch('https://api.example.com/users');
const users = await res.json();
---


  {users.map(user => 
{user.name}
)}

hard

A. Fetch data in frontmatter but forget to parse JSON

B. Fetch without await, map users directly on Promise

C. Fetch with await, parse JSON, then map users in component

D. Use fetch inside component JSX without frontmatter

Solution

1. Step 1: Fetch and parse JSON in frontmatter

   Using await fetch and await res.json() gets the user list as an array before rendering.

2. Step 2: Map over users array in component

   Mapping users to list items displays each user name correctly in the rendered HTML.

3. Final Answer:

   Fetch with await, parse JSON, then map users in component -> Option C

4. Quick Check:

   Await fetch + parse + map users = correct [OK]

Hint: Await fetch and parse JSON before mapping data [OK]

Common Mistakes:

• Mapping over unresolved Promise instead of data array
• Fetching inside JSX causing runtime errors
• Not parsing JSON before using data