Question

解构时，我不断得到public ClientResponse runAdHoc(String sql, Object... sqlArgs) throws IOException, ProcCallException { ClientConfig clientConfig = new ClientConfig(); Client voltdbClient = ClientFactory.createClient(clientConfig); voltdbClient.createConnection(voltdbServer, voltdbPort); Object[] procArgs; if (sqlArgs == null || sqlArgs.length == 0) { procArgs = new Object[1]; } else { procArgs = new Object[sqlArgs.length + 1]; System.arraycopy(sqlArgs, 0, procArgs, 1, sqlArgs.length); } procArgs[0] = sql; return voltdbClient.callProcedure("@AdHoc", procArgs); } payload：

undefined

如何检查未定义？我已经尝试过以下检查，但仍会收到错误消息：

let videosArray = [];
if (payload.videos) {
  const {
    payload: { videos }
  } = action;
  videosArray = videos;
}

return videosArray;

Answer 1

您需要定义这样的操作const action = {payload: {videos: ["Matrix", "Star Wars"]}}

您可以像这样if(action && action.payload)检查有效载荷是否未定义，然后可以执行销毁操作。

Answer 2

您只需要确保先定义动作，然后访问其参数即可，而不是自己调用有效负载。在您的示例中，当您尝试访问payload时似乎没有声明

function getVideos(action) {
  if (action && action.payload && action.payload.videos) {
    const {payload: {videos}} = action;
    return videos;
  }

  return [];
}

console.log(getVideos()); // action undefined, expected []
console.log(getVideos({})); // payload undefined, expected []
console.log(getVideos({payload: {}})); // videos undefined, expected []
console.log(getVideos({payload: {videos: [1,2,3]}})); // expected [1,2,3]

当然，如果您确实想通过分解来完成任务，则可以简单地创建一些默认值，如下所示：

function getVideos(action) {
  const {payload: {videos=[]}={}} = action || {};
  return videos;
}

console.log(getVideos()); // action undefined, expected []
console.log(getVideos({})); // payload undefined, expected []
console.log(getVideos({payload: {}})); // videos undefined, expected []
console.log(getVideos({payload: {videos: [1,2,3]}})); // expected [1,2,3]

Answer 3

您可以在不破坏结构的情况下进行检查并获得默认值。

function getVideos(action) {
    return action && action.payload && action.payload.videos || [];
}

console.log(getVideos());                 // action undefined, expected []
console.log(getVideos({}));              // payload undefined, expected []
console.log(getVideos({ payload: {} }));  // videos undefined, expected []
console.log(getVideos({ payload: { videos: [1, 2, 3] } })); // expected [1, 2, 3]

解构嵌套参数，未定义错误

3 个答案: