add_action('wp_ajax_nopriv_specs_zan', 'specs_zan');
add_action('wp_ajax_specs_zan', 'specs_zan');
function specs_zan(){
    global $wpdb,$post;
    $id = $_POST["um_id"];
    $action = $_POST["um_action"];
    if ( $action == 'ding'){
        $specs_raters = get_post_meta($id,'specs_zan',true);
        $expire = time() + 99999999;
        $domain = ($_SERVER['HTTP_HOST'] != 'localhost') ? $_SERVER['HTTP_HOST'] : false; // make cookies work with localhost
        setcookie('specs_zan_'.$id,$id,$expire,'/',$domain,false);
        if (!$specs_raters || !is_numeric($specs_raters)) {
            update_post_meta($id, 'specs_zan', 1);
        } 
        else {
            update_post_meta($id, 'specs_zan', ($specs_raters + 1));
        }
        echo get_post_meta($id,'specs_zan',true);
    } 
    die;
}

$.fn.postLike = function() {
	if ($(this).hasClass('done')) {
		alert('您已赞过该文章');
		return false;
	} else {
		$(this).addClass('done');
		var id = $(this).data("id"),
		action = $(this).data('action'),
		rateHolder = $(this).children('.count');
		var ajax_data = {
			action: "specs_zan",
			um_id: id,
			um_action: action
		};
		$.post("/wp-admin/admin-ajax.php", ajax_data,
		function(data) {
			$(rateHolder).html(data);
		});
		return false;
	}
};
$(document).on("click", ".specsZan",
	function() {
		$(this).postLike();
});

<div class="post-like">
    <a href="javascript:;" data-action="ding" data-id="<?php the_ID(); ?>" class="specsZan <?php if(isset($_COOKIE['specs_zan_'.$post->ID])) echo 'done';?>">喜欢 <span class="count">
        <?php if( get_post_meta($post->ID,'specs_zan',true) ){
            		echo get_post_meta($post->ID,'specs_zan',true);
                } else {
					echo '0';
				}?></span>
    </a>
</div>

.post-like{text-align:center;padding:10px}
.post-like a{ background-color:#21759B;border-radius: 3px;color: #FFFFFF;font-size: 12px;padding: 5px 10px;text-decoration: none;outline:none}
.post-like a.done, .post-like a:hover{background-color:#eee;color:#21759B;}	
.post-like a.done{cursor:not-allowed}