Source
File: wp-includes/media.php
function wp_img_tag_add_loading_attr( $image, $context ) {
/**
* Filters the `loading` attribute value. Default `lazy`.
*
* Returning `false` or an empty string will not add the attribute.
* Returning `true` will add the default value.
*
* @since 5.5.0
*
* @param string|bool $value The `loading` attribute value. Returning a falsey value will result in
* the attribute being omitted for the image. Default is `lazy`.
* @param string $image The HTML `img` tag to be filtered.
* @param string $context Additional context about how the function was called or where the img tag is.
*/
$value = apply_filters( 'wp_img_tag_add_loading_attr', 'lazy', $image, $context );
if ( $value ) {
if ( ! in_array( $value, array( 'lazy', 'eager' ), true ) ) {
$value = 'lazy';
}
// Images should have source and dimension attributes for the `loading` attribute to be added.
if ( false === strpos( $image, ' src="' ) || false === strpos( $image, ' width="' ) || false === strpos( $image, ' height="' ) ) {
return $image;
}
return str_replace( '<img', '<img loading="' . esc_attr( $value ) . '"', $image );
}
return $image;
}