//js
jQuery( document ).ready(function() {
    jQuery.ajax({
        url: ajaxurl,
        method: "POST",
        data: {
            name: "John",
            location: "Boston",
            action: "testing"
        },
        success: function(data) {
            alert(data);
        }
    });
})

//functions.php
add_action( 'wp_ajax_testing', 'testing' );

function testing() {
    echo $_POST['name'];
    die();
}