如何使用持有數組名稱的變量將對象文字添加到數組

Question

我在將新的對象文字放入數組時遇到麻煩。 當我使用數組名稱時，一切正常。 但是，當我切換代碼以使用保存數組名稱的變量時，它不起作用。

我有6個類似以下的數組，它們已列在我的頁面上。 單擊會將被單擊的數組的名稱保存到名為whichList的變量中。

這是三個數組：

student0 = [
  {
    status: "completed",
    goal: "go to store",
    duedate: "November 1",
    datecreated: ""
  }, {
    status: "completed",
    goal: "buy beer",
    duedate: "November 2",
    datecreated: ""
  }
];

student1 = [
  {
    status: "completed",
    goal: "go to the beach",
    duedate: "November 7"
  }, {
    status: "completed",
    goal: "swim without drowning",
    duedate: "November 8",
    datecreated: ""
  }
];

student2 = [
  {
    status: "completed",
    goal: "fly a plane",
    duedate: "November 11",
    datecreated: ""
  }, {
    status: "completed",
    goal: "don't crash",
    duedate: "November 12",
    datecreated: ""
  }
];

這是工作代碼，直接指定數組名稱。 單擊后，它將在控制台中顯示我更新的陣列：

$('#savegoal').click(function() {
  datecreated = new Date();
  student0[student0.length] = {
    status: "pending",
    goal: "\"" + $('#thegoal').val() + "\"",
    duedate: "\"" + $('#thedeadline').val() + "\"",
    datecreated: "\"" + datecreated + "\""
  };
  return console.log(student0);
});

這是無效代碼。 我想使用whichList變量。

我已經使用console.log來檢查變量是否在函數的開頭顯示了正確的數組名稱。 那里一切都很好。 但是我在控制台中得到的只是數組變量，而不是像在工作版本中那樣，數組的內容。

$('#savegoal').click(function() {
  datecreated = new Date();
  whichList[whichList.length] = {
    status: "pending",
    goal: "\"" + $('#thegoal').val() + "\"",
    duedate: "\"" + $('#thedeadline').val() + "\"",
    datecreated: "\"" + datecreated + "\""
  };
  return console.log(whichList);
});

Answer 1

您可以使用window[whichList] ，因為數組變量可能位於global / window范圍內：

var whichList = "student0";
var theList = window[whichList];
theList[theList.length] = { ... };   // consider using instead: theList.push( { ... }) 

Answer 2

您問題的直接答案：

var wichList = null;
$('#savegoal').click(function() {
  if (wichList == null){
      alert('No list selected');
  }
  // don't forget the "var", otherwise "datecreated"
  // will actually be a global variable
  var datecreated = new Date();
  // ".push()" adds the given value at the end of the array
  wichList.push({
    status: "pending",
    goal: "\"" + $('#thegoal').val() + "\"",
    duedate: "\"" + $('#thedeadline').val() + "\"",
    datecreated: "\"" + datecreated + "\""
  });
  return console.log(wichList);
});

//somewhere else in your code :
if (somecond) {
    wichList = student0;
} elseif (somecond) {
    wichList = student1;
} else {
    wichList = null;
}

上面的代碼有效：在javascript中， array變量實際上是對數組內容的引用

var a = [];
var b = a;
// b an a are now references to the same array,
// any modification to a will be "seen" by b, and vice versa :
a.push(1);
b.push(2);
// a == b == [1,2]

---

但是，給定“學生”變量的名稱，這些列表可能應該存儲在數組中：

var students = [];

students[0] = [{
    status: "completed",
    goal: "go to store",
    duedate: "November 1",
    datecreated: ""
  }, {
    status: "completed",
    goal: "buy beer",
    duedate: "November 2",
    datecreated: ""
  }];

students[1] = [ ...

現在，您可以使用此數組中的索引作為識別學生的一種方式，也許需要額外的選擇：

<select id="student">
    <option value="0">student 0</option>
    <option value="1">student 1</option>
    ...
</select>

並在您的click回調中使用它：

$('#savegoal').click(function() {
  var datecreated = new Date();
  var i = $('#student').val();
  students[i].push({
    status: "pending",
    goal: "\"" + $('#thegoal').val() + "\"",
    duedate: "\"" + $('#thedeadline').val() + "\"",
    datecreated: "\"" + datecreated + "\""
  });
  return console.log(students[i]);
});

Answer 3

首先，使用數組而不是單獨的變量：

var student = [
    [{
        status: "completed",
        goal: "go to store",
        duedate: "November 1",
        datecreated: ""
    }, {
        status: "completed",
        goal: "buy beer",
        duedate: "November 2",
        datecreated: ""
    }],
    [{
        status: "completed",
        goal: "go to the beach",
        duedate: "November 7"
    }, {
        status: "completed",
        goal: "swim without drowning",
        duedate: "November 8",
        datecreated: ""
    }],
    [{
        status: "completed",
        goal: "fly a plane",
        duedate: "November 11",
        datecreated: ""
    }, {
        status: "completed",
        goal: "don't crash",
        duedate: "November 12",
        datecreated: ""
    }],
    ...
];

然后， whichList應該是數組的索引（即從0到5的數字），而不是變量的名稱，您可以執行以下操作：

$('#savegoal').click(function() {
    datecreated = new Date().toString();
    student[whichList].push({
        status: "pending",
        goal: $('#thegoal').val(),
        duedate: $('#thedeadline').val(),
        datecreated: datecreated
    });
});

您不需要將所有這些"\\""連接起來，在鍵入字符串文字時，引號是表示法的一部分，不需要從變量或表達式中獲取字符串的內容。

如果要使用學生證作為查找每個學生的關鍵，請按以下步驟操作：

var student = {};
student[student0] = [
    {
        status: "completed",
        goal: "go to store",
        duedate: "November 1",
        datecreated: ""
    }, {
        status: "completed",
        goal: "buy beer",
        duedate: "November 2",
        datecreated: ""
    }];
student[student1] = [
    {
        status: "completed",
        goal: "go to the beach",
        duedate: "November 7"
    }, {
        status: "completed",
        goal: "swim without drowning",
        duedate: "November 8",
        datecreated: ""
    }];
student[student2] = [
    {
        status: "completed",
        goal: "fly a plane",
        duedate: "November 11",
        datecreated: ""
    }, {
        status: "completed",
        goal: "don't crash",
        duedate: "November 12",
        datecreated: ""
    }];

$('#savegoal').click(function() {
    datecreated = new Date();
    push(student[whichStudentId],{
        status: "pending",
        goal: $('#thegoal').val(),
        duedate: $('#thedeadline').val(),
        datecreated: datecreated
    });
    console.log(whichList);
});