根据Stack和ACF论坛上的一些帖子，我创建了更改lazyload脚本lozad的默认img html标记的代码。js。它工作得很好，但在管理后端也可以工作。我想用if( ! is_admin(); ) 但没有效果。我怎样才能解决这个问题？

<?php // Modify img markup for lazy load
add_filter( \'wp_get_attachment_image_attributes\', \'gs_change_attachment_image_markup\' );

function gs_change_attachment_image_markup($attributes){
    if (isset($attributes[\'src\'])) {
        $attributes[\'data-src\'] = $attributes[\'src\'];
        $attributes[\'src\']      = \'\'; //could add default small image or a base64 encoded small image here
    }
    if (isset($attributes[\'srcset\'])) {
        $attributes[\'data-srcset\'] = $attributes[\'srcset\'];
        $attributes[\'srcset\'] = \'\';
    }
    $attributes[\'class\'] .= \' lozad\';
    return $attributes;
}
add_filter(\'the_content\', \'content_image_markup\', 15);

function content_image_markup($the_content) {
$thecontent = get_the_content();
   if(!empty($thecontent)) {
        libxml_use_internal_errors(true);
        $post = new DOMDocument();
        //$post->loadHTML($the_content);
        $post->loadHTML(mb_convert_encoding($the_content, \'HTML-ENTITIES\', \'UTF-8\'));
        $imgs = $post->getElementsByTagName(\'img\');
        // Iterate each img tag
        foreach( $imgs as $img ) {
            if( $img->hasAttribute(\'data-src\') ) continue;
            if( $img->parentNode->tagName == \'noscript\' ) continue;
            $clone = $img->cloneNode();
            $src = $img->getAttribute(\'src\');
            $img->removeAttribute(\'src\');
            $img->setAttribute(\'data-src\', $src);
            $srcset = $img->getAttribute(\'srcset\');
            $img->removeAttribute(\'srcset\');
            if( ! empty($srcset)) {
                $img->setAttribute(\'data-srcset\', $srcset);
            }
            $imgClass = $img->getAttribute(\'class\');
            $img->setAttribute(\'class\', $imgClass . \' lozad\');
            $no_script = $post->createElement(\'noscript\');
            $no_script->appendChild($clone);
            $img->parentNode->insertBefore($no_script, $img);
        };
        return $post->saveHTML();
    }
}
add_filter(\'acf_the_content\', \'acf_content_image_markup\', 15);

function acf_content_image_markup($the_content) {
        libxml_use_internal_errors(true);
        $post = new DOMDocument();
        //$post->loadHTML($the_content);
        $post->loadHTML(mb_convert_encoding($the_content, \'HTML-ENTITIES\', \'UTF-8\'));
        $imgs = $post->getElementsByTagName(\'img\');
        // Iterate each img tag
        foreach( $imgs as $img ) {
            if( $img->hasAttribute(\'data-src\') ) continue;
            if( $img->parentNode->tagName == \'noscript\' ) continue;
            $clone = $img->cloneNode();
            $src = $img->getAttribute(\'src\');
            $img->removeAttribute(\'src\');
            $img->setAttribute(\'data-src\', $src);
            $srcset = $img->getAttribute(\'srcset\');
            $img->removeAttribute(\'srcset\');
            if( ! empty($srcset)) {
                $img->setAttribute(\'data-srcset\', $srcset);
            }
            $imgClass = $img->getAttribute(\'class\');
            $img->setAttribute(\'class\', $imgClass . \' lozad\');
            $no_script = $post->createElement(\'noscript\');
            $no_script->appendChild($clone);
            $img->parentNode->insertBefore($no_script, $img);
        };
        return $post->saveHTML();
}
function image_tag_class($class, $id, $align, $size) {
  return $class . \' lozad\';
}
add_filter(\'get_image_tag_class\', \'image_tag_class\', 10, 4);

?>