Simple WordPress ajax structure example

wp_ajax_request

<?php
// in functions.php 

add_action('wp_ajax_testing_axaj', 'ajax_function_to_execute', 1, 2);
add_action('wp_ajax_nopriv_testing_axaj', 'ajax_function_to_execute', 1, 2);
function ajax_function_to_execute() {

  print_r($_REQUEST);
  die();

}

// Add your js file where you need it
add_action( 'admin_enqueue_scripts', 'enqueue_my_scripts' );
function enqueue_my_scripts($hook) {
    if( 'index.php' != $hook ) {
	    // Do not execute in the dashboard
	    return;
    }
	wp_enqueue_script( 'my-ajax-script', plugins_url( get_stylesheet_directory_uri().'/js/my-ajax-script.js' ), array('jquery') );

?>

<?php // Recommended the following go in its own js file you enqueue with above php function ?>
<script type="text/javascript">
jQuery(document).ready(function($) {
	var data = {
		action: 'testing_axaj',
		arbitrary_value: 'arbitrary_key'
	};

  $.ajax({
    url: window.ajaxurl,
    data: data,
    async: true,
    cache: false,
    type:  'get',
    success: function(response){
      console.log('Response from server: ' + response);
    }
  });
});
</script>