Functions to add a custom route to the WP REST API

WP-custom_rest_api.php

// Init REST Route
function register_custom_api_hooks() {
    $namespace = 'custom-name/v1';

    register_rest_route( $namespace, '/posts/', array(
        'methods' => 'GET',
        'callback' => 'custom_api_get_posts',
    ) );
}
add_action( 'rest_api_init', 'register_custom_api_hooks' );

// Callback Function to get posts
function custom_api_get_posts() {
    $args = array(
        'numberposts' => 10,
        'post_type' => 'post',
        'post_status' => 'publish',
    );
    $all_posts = get_posts( $args );
    $return = array();
    foreach ( $all_posts as $post ) {
        $return[] = array(
            'ID' => $post->ID,
            'title' => $post->post_title,
            'permalink' => get_permalink( $post->ID ),
        );
    }

    $response = new WP_REST_Response( $return );
    $response->header( 'Access-Control-Allow-Origin', '*' );
    return $response;
}