/**//* * Returns a function that waits for the specified XMLHttpRequest * to complete, then passes its XML response to the given handler function. * req - The XMLHttpRequest whose state is changing * responseXmlHandler - Function to pass the XML response to */ function getReadyStateHandler(req, responseXmlHandler) { ??// 返回一个监听XMLHttpRequest实例的匿名函数 ??return function () { ????// 如果请求的状态是“完成” ????if (req.readyState ==4) { ??????// 检查是否成功接收了服务器响应 ??????if (req.status ==200)