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Basic Questions for WordPress REST API Interview FAQs

Frequently asked interview questions about the WordPress REST API, covering concepts, practical implementation, and advanced topics:

Q. What is the WordPress REST API?

The WordPress REST API is a way to interact with WordPress data using JSON. It allows developers to create, read, update, and delete WordPress resources programmatically.

Q. What is the default URL for accessing the WordPress REST API?

The base URL is:

http://your-site.com/wp-json/

Q. What are some common use cases of the WordPress REST API?

Building headless CMS applications.

Integrating WordPress with third-party applications or services.

Creating custom mobile or desktop applications.

Fetching or sending data programmatically for plugins or themes.

Q. What are endpoints in the WordPress REST API?

Endpoints are specific URLs that represent objects or actions. For example:

Get all posts: GET /wp-json/wp/v2/posts

Get a specific post: GET /wp-json/wp/v2/posts/{id}

Q. What are the HTTP methods supported by the WordPress REST API?

Common methods include:

GET: Retrieve data.

POST: Create data.

PUT/PATCH: Update data.

DELETE: Remove data.

Intermediate Questions

Q. How do you authenticate requests in the WordPress REST API?

Authentication methods include:

Cookie Authentication: For logged-in users.

Basic Authentication: Using a username and password (for testing purposes).

OAuth: For secure and scalable authentication.

Application Passwords: Built into WordPress for specific API requests.

JWT (JSON Web Token): A common method for secure APIs.

Q. How do you register a custom REST API endpoint?

Use the register_rest_route() function in a plugin or theme:

add_action('rest_api_init', function () {
    register_rest_route('myplugin/v1', '/data', [
        'methods' => 'GET',
        'callback' => 'my_custom_callback',
]);
});
function my_custom_callback() {
    return ['message' => 'Hello World!'];
}

Q. How do you include custom fields in REST API responses?

Use the register_rest_field() function:

add_action('rest_api_init', function () {
    register_rest_field('post', 'custom_field', [
        'get_callback' => 'get_post_custom_field',
        'schema' => null,
]);
});
function get_post_custom_field($object) {
    return get_post_meta($object['id'], 'custom_field_key', true);
}

Q. How do you restrict access to an endpoint in the REST API?

Use the permission_callback parameter:

add_action('rest_api_init', function () {
    register_rest_route('myplugin/v1', '/private', [
        'methods' => 'GET',
        'callback' => 'my_private_callback',
        'permission_callback' => 'is_user_logged_in',
]);
});

Q. How do you handle pagination in the WordPress REST API?

Pagination parameters include:

?page=2: To fetch the second page.

?per_page=10: To fetch 10 results per page.

Advanced Questions

Q. How do you disable the WordPress REST API?

Use the following code snippet to disable REST API access:

add_filter('rest_authentication_errors', function ($result) {
    if (!is_user_logged_in()) {
        return new WP_Error('rest_forbidden', 'REST API access is restricted.', ['status' => 403]);
}
    return $result;
});

Q. How can you modify the default REST API query for posts?

Use the rest_post_query filter:

add_filter('rest_post_query', function ($args, $request) {
    $args['orderby'] = 'title';
    $args['order'] = 'ASC';
    return $args;
}, 10, 2);

Q. What is the purpose of the _embed parameter in the REST API?

The _embed parameter is used to include additional related data in API responses, such as featured images or taxonomy terms:

GET /wp-json/wp/v2/posts?_embed

Q. How do you handle CORS (Cross-Origin Resource Sharing) in the REST API?

Add CORS headers:

add_action('rest_api_init', function () {
    header("Access-Control-Allow-Origin: *");
    header("Access-Control-Allow-Methods: GET, POST, PUT, DELETE");
});

Q. What are the limitations of the WordPress REST API?

Lack of granular permission control for endpoints.

Potential performance issues for large-scale queries without proper optimization.

Limited out-of-the-box features for advanced use cases like batch processing.

Scenario-Based Questions

Q. How would you use the REST API to create a decoupled frontend?

Fetch WordPress data using REST API endpoints in frameworks like React or Vue.js.

Use libraries like Axios or Fetch API for HTTP requests.

Example in React:

fetch('https://example.com/wp-json/wp/v2/posts')
.then(response => response.json())
.then(data => console.log(data));

Q. How do you extend the REST API for a custom post type?

Ensure 'show_in_rest' => true is set when registering the post type:

register_post_type ('book', [
'public' => true==,
    'show_in_rest' => true,
    'label' => 'Books',
]);

Q. How would you troubleshoot REST API 404 errors?

Check permalink settings.

Ensure the REST API is enabled and the rest_route parameter is accessible.

Look for conflicts with plugins or themes.

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