百度ueditor组件上传图片后如何设置img里的alt属性

function callback(){
try{
var link, json, loader,
body = (iframe.contentDocument || iframe.contentWindow.document).body,
result = body.innerText || body.textContent || '';
json = (new Function("return " + result))();
link = me.options.imageUrlPrefix + json.url;
if(json.state == 'SUCCESS' && json.url) {
loader = me.document.getElementById(loadingId);
loader.setAttribute('src', link);
loader.setAttribute('_src', link);
loader.setAttribute('title', json.title || '');
loader.setAttribute('alt', json.original || '');
loader.removeAttribute('id');
domUtils.removeClasses(loader, 'loadingclass');
} else {
showErrorLoader && showErrorLoader(json.state);
}
}catch(er){
showErrorLoader && showErrorLoader(me.getLang('simpleupload.loadError'));
}
form.reset();
domUtils.un(iframe, 'load', callback);
}