WordPress 后台发布文章时提示用户选择分类

/**
 * WordPress 发布文章前必须选择分类
 * https://www.wpdaxue.com/choose-a-category-before-publish.html
 */
add_action('admin_footer-post.php', 'choose_a_category_before_publish');
add_action('admin_footer-post-new.php', 'choose_a_category_before_publish');
function choose_a_category_before_publish(){
	global $post_type;
	if($post_type=='post'){
		echo "<script>
jQuery(function($){
	$('#publish, #save-post').click(function(e){
		if($('#taxonomy-category input:checked').length==0){
			alert('抱歉，发布文章前，请选择一个分类');
			e.stopImmediatePropagation();
			return false;
		}else{
			return true;
		}
	});
	var publish_click_events = $('#publish').data('events').click;
	if(publish_click_events){
		if(publish_click_events.length>1){
			publish_click_events.unshift(publish_click_events.pop());
		}
	}
	if($('#save-post').data('events') != null){
		var save_click_events = $('#save-post').data('events').click;
		if(save_click_events){
		  if(save_click_events.length>1){
			  save_click_events.unshift(save_click_events.pop());
		  }
		}
	}
});
</script>";
	}
}