我 JSON.stringify 一個對象，但如何在 Javascript 中打印出對象的特定元素

Question

javascript 和以下代碼的新手我正在嘗試打印出對象中的某些內容。

           firebase.database().ref('/userProfile/').orderByChild('eventList').once('value', (snapshot) => {
  this.users = [];
  snapshot.forEach((childSnapshot) => {
    var list = childSnapshot.val();
    console.log(JSON.stringify(list.eventList, null, 2));

下面是控制台中使用上述代碼打印的一個對象的示例，但如何僅打印日期、描述、位置、名稱和價格而不帶括號。 我嘗試做 list.eventList.date 但說日期未定義。 我也試過 console.log(list.eventList[0].date) 但返回無法讀取未定義的屬性 '0' 在 snapshot.forEach

             {
    "-L5niHTgOezEJWI8ge6O": {
    "date": "2018-02-20",
      "description": "lijliil",
        "location": "lijli",
          "name": "jiji",
       "numOfTickets": "9",
        "price": "7",
     "tickets": [
             0,
             1,
             2,
             3,
             ]
            }
           }

下面是我的 firebase 數據庫的一部分。

  {
  "userProfile" : {
"3RQOUe9cqcRX2IMy0S290S9trSM2" : {
  "birthDate" : "2018-02-20",
  "email" : "acs@acs.com",
  "firstName" : "asda",
  "lastName" : "dsad",
  "userType" : "customer"
},
"9VvVRfTt7sPayXuifhBYrincYs12" : {
  "birthDate" : "2018-02-20",
  "email" : "testmail@email.com",
  "eventList" : {
    "-L5nEpqLyOO5hid53lf8" : {
      "date" : "2018-08-16",
      "description" : "drake ",
      "location" : "02 dublin",
      "name" : "drake",
      "numOfTickets" : "10",
      "price" : "80",
      "tickets" : [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ]
            },

當我 console.log(JSON.stringify(list, null, 2)); 我得到了一切，但我只想打印出每個用戶的每個事件列表

        {
    "birthDate": "2018-02-20",
    "email": "liam@user1.com",
    "eventList": {
        "-L5nUpmVU3NUgeUWYvcN": {
            "date": "2018-02-20",
            "description": "ijdljdlijf",
            "location": "dublin",
            "name": "liam",
            "numOfTickets": "12",
            "price": "123",
            "tickets": [
                0,
                1,
                2,
                3,
                4,
                5,
                6,
                7,
                8,
                9,
                10,
                11
            ]
        },
        "-L5nWt640bwKAGwZ-rwZ": {
            "date": "2018-02-20",
            "description": "uhkuh",
            "location": "khuuh",
            "name": "xsacs",
            "numOfTickets": "4",
            "price": "12",
            "tickets": [
                0,
                1,
                2,
                3
            ]
        }
    },
    "firstName": "liam",
    "lastName": "mcaweeney",
    "userType": "eventorganiser"
}

我嘗試將對象轉換為數組，但說 ERROR TypeError: Cannot convert undefined or null to object at Function.keys ()

               snapshot.forEach((childSnapshot) => {
    var data = childSnapshot.val();
    var eventList = data.eventList;

    const eventListArray = Object.keys(eventList).map(i => eventList[i])

    console.log(eventListArray[0].date) 

Answer 1

您需要將對象轉換為數組對象並訪問它。

 var data = { "birthDate": "2018-02-20", "email": "liam@user1.com", "eventList": { "-L5nUpmVU3NUgeUWYvcN": { "date": "2018-02-20", "description": "ijdljdlijf", "location": "dublin", "name": "liam", "numOfTickets": "12", "price": "123", "tickets": [ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 ] }, "-L5nWt640bwKAGwZ-rwZ": { "date": "2018-02-20", "description": "uhkuh", "location": "khuuh", "name": "xsacs", "numOfTickets": "4", "price": "12", "tickets": [ 0, 1, 2, 3 ] } }, "firstName": "liam", "lastName": "mcaweeney", "userType": "eventorganiser" } var eventList = data.eventList; const eventListArray = Object.keys(eventList).map(i => eventList[i]) console.log(eventListArray[0].date)