scalajs在ajax.post onfailure上获取原因

尝试找出ajax.post失败的原因(使用scala.js),但只获取类名:

Ajax.post(
  url = "...",
  data = "...",
  headers = Map("Content-Type"->"application/json; charset=utf-8",
                "Csrf-Token" -> "...")
).map(_.responseText).map(
  content => content match {
    case _                  => ...
  }
).onFailure {
  case err => log.info(s"failure ${err.toString} ${err.getCause} ${err.getMessage}")
}

我得到:

failure org.scalajs.dom.ext.AjaxException null null

有可能找到原因吗? 谢谢