Ajax in Wordpress in wordpress way

<script type="text/javascript">
                jQuery(document).ready(function($) {
                    //console.log('ready');
                    jQuery("#cbrpsearchfieldbt").click(function(){
                        $("#cbrpsearchfield").keypress();
                    });

                    $("#cbrpsearchfield").keypress(function() {
                        var cbrpsearchterm = jQuery("#cbrpsearchfield").val();
                        //console.log(cbrpsearchterm);
                        //console.log(cbrpsearchterm.length);
                        if(cbrpsearchterm.length > 2){
                            //console.log('click');
                            var data = {
                                    action: 'cbrelatedpostajax',
                                    rpsearchterm:cbrpsearchterm,
                                    postid:<?php echo $post->ID; ?>
                            };

                            // since 2.8 ajaxurl is always defined in the admin header and points to admin-ajax.php
                            jQuery.post(ajaxurl, data, function(response) {
                                    //alert('Got this from the server: ' + response);
                                    jQuery('#cbrelatedpostsresult').html(response);
                            });
                        }
                    })

                });
            </script>



if( is_admin() )
{
    add_action('wp_ajax_cbrelatedpostajax', 'cbrelatedpostajax_callback');

    // Load "admin-only" scripts here
}

function cbrelatedpostajax_callback(){
    ob_clean();
    $rpsearchterm =  $_POST['rpsearchterm'] ;
    $postid       =  $_POST['postid'];
    $cbargs = array('post_type' => 'product', 'post_status' => 'publish', 'orderby' => 'date', 'order'  => 'DESC', 'posts_per_page'  => 20, 's' => $rpsearchterm );
    $upprev_query = new WP_Query( $cbargs );
    if ($upprev_query->have_posts()) {
        while ( $upprev_query->have_posts() ) {
            $upprev_query->the_post();
            $id = get_the_ID();
            if($postid != $id )echo '<li>'.get_the_title().' - '. $id .'</li>';
        }
    }
    else echo '<li>No search result found</li>';

    die();
}