WordPress/wp-admin/js/set-post-thumbnail.js

function WPSetAsThumbnail(id){var $link=jQuery("#media-item-"+id+" a.wp-post-thumbnail");$link.text(setPostThumbnailL10n.saving);jQuery.post(ajaxurl,{action:"set-post-thumbnail",post_id:post_id,thumbnail_id:id,cookie:encodeURIComponent(document.cookie)},function(str){var win=window.dialogArguments||opener||parent||top;$link.text(setPostThumbnailL10n.setThumbnail);if(str=="0"){alert(setPostThumbnailL10n.error)}else{jQuery("a.wp-post-thumbnail").show();$link.hide();win.WPSetThumbnailID(id);win.WPSetThumbnailHTML(str)}})};