WordPress AJAX Frontend Execution

frontend-ajax.php

<?php
/**
 * WordPress AJAX Frontend Execution.
 *
 * Using WP Ajax should not be used from the frontend because response
 * from `admin-ajax.php` are not cached (including `nocache_headers()`).
 * Instead, you should add a query var, and then do the `template_include`
 * routine to select a template that returns JSON.
 *
 * A side benefit here is that it makes your site more RESTful.
 */

function wp_ajax_query_vars( $vars ){
	$vars[] = 'wp_ajax_action';
	return $vars;
}
add_filter( 'query_vars', 'wp_ajax_query_vars' );

public function wp_ajax_callback( $template ) {
	$wp_ajax_action = get_query_var( 'wp_ajax_action' );

	if ( $wp_ajax_action ) {
		// Executing AJAX process
		define( 'DOING_AJAX', true );

		if ( ! has_action( 'wp_ajax_' . $wp_ajax_action ) && ! has_action( 'wp_ajax_nopriv_' . $wp_ajax_action ) ) {
			// No ajax action found
			status_header( 404 );
			wp_send_json_error();
		}

		if ( is_user_logged_in() ) {
			/**
			 * Fires authenticated AJAX actions for logged-in users.
			 *
			 * The dynamic portion of the hook name, $wp_ajax_action,
			 * refers to the name of the AJAX action callback being fired.
			 *
			 * @since 4.1.0
			 */
			do_action( 'wp_ajax_' . $wp_ajax_action );
		} else {
			/**
			 * Fires non-authenticated AJAX actions for logged-out users.
			 *
			 * The dynamic portion of the hook name, $wp_ajax_action,
			 * refers to the name of the AJAX action callback being fired.
			 *
			 * @since 4.1.0
			 */
			do_action( 'wp_ajax_nopriv_' . $wp_ajax_action );
		}
	}

	return $template
}
add_filter( 'template_include', array( $this, 'wp_ajax_callback' ) );

/**
 * Example usage.
 */
function example_frontend_ajax_enqueue() {
	wp_enqueue_script( 'ajax-script', plugins_url( '/js/my_script.js', __FILE__ ) );

	$ajax_url = add_query_arg( array( 'wp_ajax_action', 'my_action' ), get_home_url() );

	// in JavaScript, object properties are accessed as window.ajaxurl
	wp_localize_script( 'ajax-script', 'window', array( 'ajaxurl' => $ajax_url ) );
}
add_action( 'enqueue_scripts', 'example_frontend_ajax_enqueue' );

function example_frontend_ajax_callback() {
	/*
	 * Do stuff
	 */

	wp_send_json_success();
}
add_action( 'wp_ajax_my_action', 'example_frontend_ajax_callback' );
add_action( 'wp_ajax_nopriv_my_action', 'example_frontend_ajax_callback' );