PHP 404判断 与 js 404判断

php判断404：

$url = home_url()."/wp-content/themes/twentythirteen/pic/".$result['pic'];
							$headers = @get_headers($url);
							if(strpos($headers[0],'404') )
							{
								$url=home_url()."/wp-content/themes/twentythirteen/pic/default.png";
							}

js判断404：

var pic_url ="/wp-content/themes/twentythirteen/pic/"+data[i].pic;
			$.ajax({
				url:pic_url,
				error:function(xhr, error, ex){
					if (xhr.status == '404') {
						pic_url = "/wp-content/themes/twentythirteen/pic/default.png";
					}
				},
				success:function(){
					pic_url = pic_url;
				}
			});

js判断404,要通过ajax......