概述

wp_get_loading_attr_default() 函数用于获取元素 loading 属性的默认值，通常返回 'lazy'，但会根据上下文和启发式规则判断是否省略该属性以优化性能。该函数自 WordPress 6.3.0 起已弃用，建议使用 wp_get_loading_optimization_attributes() 替代。

关键要点

• 函数返回 'lazy'、'eager' 或布尔值 false，false 表示应省略 loading 属性。
• 通过 wp_increase_content_media_count() 计数内容媒体元素，默认前 3 个元素会省略 loading 属性，可通过 'wp_omit_loading_attr_threshold' 过滤器自定义阈值。
• 针对特定上下文（如 'template'、'template_part_header'、'the_content'、'the_post_thumbnail'）有特殊处理逻辑，以避免对首屏元素进行懒加载。
• 函数已弃用，开发者应迁移至 wp_get_loading_optimization_attributes()。

代码示例

function wp_get_loading_attr_default( $context ) {
	_deprecated_function( __FUNCTION__, '6.3.0', 'wp_get_loading_optimization_attributes()' );
	global $wp_query;

	// Skip lazy-loading for the overall block template, as it is handled more granularly.
	if ( 'template' === $context ) {
		return false;
	}

	/*
	 * Do not lazy-load images in the header block template part, as they are likely above the fold.
	 * For classic themes, this is handled in the condition below using the 'get_header' action.
	 */
	$header_area = WP_TEMPLATE_PART_AREA_HEADER;
	if ( "template_part_{$header_area}" === $context ) {
		return false;
	}

	// Special handling for programmatically created image tags.
	if ( 'the_post_thumbnail' === $context || 'wp_get_attachment_image' === $context ) {
		/*
		 * Skip programmatically created images within post content as they need to be handled together with the other
		 * images within the post content.
		 * Without this clause, they would already be counted below which skews the number and can result in the first
		 * post content image being lazy-loaded only because there are images elsewhere in the post content.
		 */
		if ( doing_filter( 'the_content' ) ) {
			return false;
		}

		// Conditionally skip lazy-loading on images before the loop.
		if (
			// Only apply for main query but before the loop.
			$wp_query->before_loop && $wp_query->is_main_query()
			/*
			 * Any image before the loop, but after the header has started should not be lazy-loaded,
			 * except when the footer has already started which can happen when the current template
			 * does not include any loop.
			 */
			&& did_action( 'get_header' ) && ! did_action( 'get_footer' )
		) {
			return false;
		}
	}

	/*
	 * The first elements in 'the_content' or 'the_post_thumbnail' should not be lazy-loaded,
	 * as they are likely above the fold.
	 */
	if ( 'the_content' === $context || 'the_post_thumbnail' === $context ) {
		// Only elements within the main query loop have special handling.
		if ( is_admin() || ! in_the_loop() || ! is_main_query() ) {
			return 'lazy';
		}

		// Increase the counter since this is a main query content element.
		$content_media_count = wp_increase_content_media_count();

		// If the count so far is below the threshold, return `false` so that the `loading` attribute is omitted.
		if ( $content_media_count < wp_omit_loading_attr_threshold() ) {
			return false;
		}
	}

	return 'lazy';
}

注意事项

• 函数仅在懒加载全局启用时调用，需确保上下文参数正确传递。
• 弃用状态意味着未来版本可能移除，建议及时更新代码以避免兼容性问题。
• 内部依赖多个 WordPress 核心函数（如 wp_increase_content_media_count()、in_the_loop() 等），调用时需注意环境条件。