REST API with JavaScript in Wordpress - Mini Project: Build & Apply

REST API with JavaScript in WordPress

📖 Scenario: You are building a simple WordPress site feature that fetches and shows the latest blog posts using the WordPress REST API and JavaScript.

🎯 Goal: Create a JavaScript script that fetches the latest 3 posts from the WordPress REST API and displays their titles in a list on the webpage.

📋 What You'll Learn

Use the WordPress REST API endpoint /wp-json/wp/v2/posts

Fetch exactly 3 posts

Display the post titles inside an unordered list <ul>

Use modern JavaScript with fetch and async/await

Add a container <div id="post-list"> in HTML to show the posts

💡 Why This Matters

🌍 Real World

Fetching and showing WordPress posts dynamically helps keep your site content fresh without manual updates.

💼 Career

Understanding how to use REST APIs with JavaScript is essential for modern web development and integrating with platforms like WordPress.

1

HTML Setup for Post List Container

Create a div element with id="post-list" in the HTML body where the post titles will appear.

Wordpress

    
    
    WordPress Posts


    

Hint

Use a div tag with the exact id="post-list" inside the body.

2

Set the API Endpoint URL

In a new <script> tag before the closing </body>, create a constant variable called apiUrl and set it to the string "https://example.com/wp-json/wp/v2/posts?per_page=3".

Wordpress

    
    
    WordPress Posts


    

    
    // Create a constant apiUrl with the WordPress REST API URL for 3 posts
    

Hint

Use const apiUrl = "https://example.com/wp-json/wp/v2/posts?per_page=3"; inside a <script> tag.

3

Fetch Posts and Extract Titles

Inside the <script> tag, write an async function called loadPosts that uses fetch(apiUrl) and await to get the response. Then convert the response to JSON and store it in a variable called posts. Use a for...of loop with post to iterate over posts and create an array called titles containing each post's title.rendered.

Wordpress

    
    
    WordPress Posts


    

    
    const apiUrl = "https://example.com/wp-json/wp/v2/posts?per_page=3";

    // Write async function loadPosts to fetch and extract titles
    

Hint

Use async function loadPosts(), await fetch(apiUrl), and a for...of loop to fill titles with post.title.rendered.

4

Display Titles in the HTML List

Still inside the loadPosts function, select the div with id="post-list" into a variable called postList. Create a string variable html that starts with "

". Use a for...of loop with title over titles to add each title inside <li> tags to html. After the loop, add "

" to html. Finally, set postList.innerHTML = html. Call loadPosts() after the function definition.

Wordpress

    
    
    WordPress Posts


    

    
    const apiUrl = "https://example.com/wp-json/wp/v2/posts?per_page=3";

    async function loadPosts() {
        const response = await fetch(apiUrl);
        const posts = await response.json();
        const titles = [];
        for (const post of posts) {
            titles.push(post.title.rendered);
        }
        // Add code here to create html list and set innerHTML
    }

    // Call loadPosts here
    

Hint

Use document.getElementById("post-list"), build html string with <ul> and <li>, then set postList.innerHTML. Call loadPosts() to run.

Practice

1. What is the main purpose of using the WordPress REST API with JavaScript?

easy

A. To get or send data to the WordPress server without reloading the page

B. To change the WordPress theme colors

C. To install WordPress plugins automatically

D. To create new WordPress users manually

Solution

1. Step 1: Understand REST API role

   The REST API allows JavaScript to communicate with the server asynchronously.

2. Step 2: Identify the purpose in WordPress context

   It is used to get or send data like posts or pages without reloading the page.

3. Final Answer:

   To get or send data to the WordPress server without reloading the page -> Option A

4. Quick Check:

   REST API = Data exchange without reload [OK]

Hint: REST API means data exchange without page reload [OK]

Common Mistakes:

• Thinking REST API changes themes or plugins
• Confusing REST API with WordPress admin tasks
• Assuming REST API reloads the page

2. Which of the following is the correct way to fetch posts from the WordPress REST API using JavaScript?

easy

A. fetch('/wp-json/wp/v2/posts').then(response => response.json())

B. fetch('wp-json/wp/v2/posts').json()

C. fetch('/wp-json/wp/v2/posts').json()

D. fetch('/wp-json/wp/v2/posts').then(response => response.text())

Solution

1. Step 1: Check fetch URL format

   The URL must start with a slash '/' to indicate root path: '/wp-json/wp/v2/posts'.

2. Step 2: Use correct response method

   Use response.json() inside a then() to parse JSON data correctly.

3. Final Answer:

   fetch('/wp-json/wp/v2/posts').then(response => response.json()) -> Option A

4. Quick Check:

   fetch + .then + response.json() = correct syntax [OK]

Hint: Use .then(response => response.json()) after fetch [OK]

Common Mistakes:

• Missing leading slash in URL
• Calling .json() directly on fetch without then
• Using response.text() instead of response.json()

3. What will the following code output if the REST API returns two posts with titles 'Hello' and 'World'?

fetch('/wp-json/wp/v2/posts')
  .then(res => res.json())
  .then(posts => {
    posts.forEach(post => console.log(post.title.rendered));
  });

medium

A. undefined\nundefined

B. posts.forEach is not a function

C. Hello\nWorld

D. Error: Cannot read property 'rendered' of undefined

Solution

1. Step 1: Understand fetch and JSON parsing

   The fetch gets posts, then res.json() parses the JSON array of posts.

2. Step 2: Loop through posts and log titles

   posts.forEach logs each post's title.rendered, so it prints 'Hello' and 'World'.

3. Final Answer:

   Hello\nWorld -> Option C

4. Quick Check:

   posts.forEach + post.title.rendered = Hello and World [OK]

Hint: Use console.log inside forEach to print each post title [OK]

Common Mistakes:

• Assuming posts is not an array
• Forgetting to parse JSON with res.json()
• Accessing title without .rendered property

4. Identify the error in this code snippet that tries to fetch pages from WordPress REST API:

async function getPages() {
  const response = await fetch('wp-json/wp/v2/pages');
  const data = await response.json;
  console.log(data);
}

medium

A. The function should not be async

B. The fetch URL is missing a leading slash '/' and response.json is missing parentheses

C. console.log should be before fetch call

D. response.json should be replaced with response.text

Solution

1. Step 1: Check fetch URL format

   The URL 'wp-json/wp/v2/pages' is missing a leading slash '/' which is required for root-relative path.

2. Step 2: Check response.json usage

   response.json is a function and must be called with parentheses: response.json()

3. Final Answer:

   The fetch URL is missing a leading slash '/' and response.json is missing parentheses -> Option B

4. Quick Check:

   URL slash + response.json() needed [OK]

Hint: Always add '/' before REST API path and call .json() as function [OK]

Common Mistakes:

• Forgetting parentheses on response.json
• Missing leading slash in URL
• Misplacing console.log before data is fetched

5. You want to fetch posts and display only those with the word 'JavaScript' in the title using async/await. Which code correctly filters and logs these posts?

hard

A. async function fetchJSPosts() {
const res = await fetch('/wp-json/wp/v2/posts');
const posts = await res.text();
const filtered = posts.filter(post => post.title.rendered.includes('JavaScript'));
filtered.forEach(post => console.log(post.title.rendered));
}

B. async function fetchJSPosts() {
const res = await fetch('/wp-json/wp/v2/posts');
const posts = await res.json;
const filtered = posts.filter(post => post.title.includes('JavaScript'));
filtered.forEach(post => console.log(post.title.rendered));
}

C. async function fetchJSPosts() {
const res = await fetch('/wp-json/wp/v2/posts');
const posts = await res.json();
const filtered = posts.filter(post => post.title.rendered == 'JavaScript');
filtered.forEach(post => console.log(post.title.rendered));
}

D. async function fetchJSPosts() {
const res = await fetch('/wp-json/wp/v2/posts');
const posts = await res.json();
const filtered = posts.filter(post => post.title.rendered.includes('JavaScript'));
filtered.forEach(post => console.log(post.title.rendered));
}

Solution

1. Step 1: Correctly fetch and parse JSON

   Use await res.json() to parse the response as JSON array of posts.

2. Step 2: Filter posts by checking if title.rendered includes 'JavaScript'

   Use posts.filter with post.title.rendered.includes('JavaScript') to select matching posts.

3. Step 3: Log filtered post titles

   Use forEach to log each filtered post's title.rendered.

4. Final Answer:

   async function fetchJSPosts() { const res = await fetch('/wp-json/wp/v2/posts'); const posts = await res.json(); const filtered = posts.filter(post => post.title.rendered.includes('JavaScript')); filtered.forEach(post => console.log(post.title.rendered)); } -> Option D

5. Quick Check:

   await fetch + .json() + filter + includes = async function fetchJSPosts() { const res = await fetch('/wp-json/wp/v2/posts'); const posts = await res.json(); const filtered = posts.filter(post => post.title.rendered.includes('JavaScript')); filtered.forEach(post => console.log(post.title.rendered)); } [OK]

Hint: Use .json() and filter with includes() on title.rendered [OK]

Common Mistakes:

• Forgetting parentheses on json()
• Using == instead of includes for substring
• Parsing response as text instead of JSON