REST API Endpoint Example

functions.php

<?php
add_action( 'rest_api_init', 'spe_register_api_hooks' );
function spe_register_api_hooks() {
	$namespace = 'simple-posts/v1';
	register_rest_route( $namespace, '/list-posts/', array(
		'methods'  => 'GET',
		'callback' => 'spe_get_posts',
	) );
}
function spe_get_posts() {
	if ( 0 || false === ( $return = get_transient( 'spe_all_posts' ) ) ) {
		$query     = apply_filters( 'spe_get_posts_query', array(
			'numberposts' => 10,
			'post_type'   => 'post',
			'post_status' => 'publish',
		) );
		$all_posts = get_posts( $query );
		$return    = array();
		foreach ( $all_posts as $post ) {
			$return[] = array(
				'ID'        => $post->ID,
				'title'     => $post->post_title,
				'permalink' => get_permalink( $post->ID ),
			);
		}
		// cache for 10 minutes
		set_transient( 'spe_all_posts', $return, apply_filters( 'spe_posts_ttl', 60 * 10 ) );
	}
	$response = new WP_REST_Response( $return );
	$response->header( 'Access-Control-Allow-Origin', apply_filters( 'spe_access_control_allow_origin', '*' ) );
	return $response;
}

main.js

	var apiPath = 'https://mckernan.in/wp-json/simple-posts/v1/list-posts',

	$.ajax({
		type : 'GET',
		url : apiPath,
		async : true,
		dataType : 'json',
		success : function(result) {
			console.log('Woohoo! We got some posts!');
			console.log(result);
		},
		fail : function(result) {
			console.log('Oh no! Something went wrong!');
			console.log(result);
		}
	});