JavaScript-“变量未定义"在循环的一部分中，在另一部分中工作 [英] JavaScript - "variable undefined" in one part of loop, working in a different part

问题描述

使用以下代码，出现此错误RewardPurchases.PurchasesArray[i].Student_Name is undefined:

Using the following code, I'm getting this error RewardPurchases.PurchasesArray[i].Student_Name is undefined:

$('button#random').click( function() {
    var Num = Math.floor(Math.random() * Total+1);
    Num--;

    for (var i in RewardPurchases.PurchasesArray) {
/* --------> */     
        $('#display').text("Ticker number " + Num + " in the LEAP database belongs to...\n\n\n" + RewardPurchases.PurchasesArray[i].Student_Name.toUpperCase() + " (" + TutorGroup + ")").show().delay(300);

        if (i == Num) {
            var TutorGroup = '';

            Frog.API.get('timetable.getClasses',
            {
                'params': {'student': RewardPurchases.PurchasesArray[i].Student_ID },
                'onSuccess': function(data) {
                    for (var i = 0; i < data.length; i++) {
                        if (data[i].subject.name == "Tut Period") {
                            TutorGroup = data[i].name.replace("/Tp", "");
                        }
                    }
                }
            });

            $('#display').animate({'font-size': 36}, 1500, function() {
                $(this).prepend('<p>!!! WINNER !!!</p>');
            });

            alert("Ticker number " + Num + " in the LEAP database belongs to...\n\n\n" + RewardPurchases.PurchasesArray[i].Student_Name.toUpperCase() + " (" + TutorGroup + ")");
        }
    }
} );

但是，如果我按如下所示移动此行$('#display').text(...，该错误就会消失:

However, if I move this line $('#display').text(... as follows, the error disappears:

$('button#random').click( function() {
    var Num = Math.floor(Math.random() * Total+1);
    Num--;

    for (var i in RewardPurchases.PurchasesArray) {

        if (i == Num) {
            var TutorGroup = '';
/* --------> */         
            $('#display').text("Ticker number " + Num + " in the LEAP database belongs to...\n\n\n" + RewardPurchases.PurchasesArray[i].Student_Name.toUpperCase() + " (" + TutorGroup + ")").show().delay(300);

            Frog.API.get('timetable.getClasses',
            {
                'params': {'student': RewardPurchases.PurchasesArray[i].Student_ID },
                'onSuccess': function(data) {
                    for (var i = 0; i < data.length; i++) {
                        if (data[i].subject.name == "Tut Period") {
                            TutorGroup = data[i].name.replace("/Tp", "");
                        }
                    }
                }
            });

            $('#display').animate({'font-size': 36}, 1500, function() {
                $(this).prepend('<p>!!! WINNER !!!</p>');
            });

            alert("Ticker number " + Num + " in the LEAP database belongs to...\n\n\n" + RewardPurchases.PurchasesArray[i].Student_Name.toUpperCase() + " (" + TutorGroup + ")");
        }
    }
} );

我不明白为什么会这样? i语句未定义i吗?

I don't understand why this is the case? i isn't being defined by the if statement?

我正在尝试在数组中显示每个名称，然后选择一个随机名称并使用"WINNER！"将其显示为大字体.在它上面.

I'm trying to display each name in an array, before picking a random name and displaying it in a large font with "WINNER!" above it.

预先感谢

推荐答案

您的数组的完整性如何?

What is the integrity of your array like?

//RewardPurchases.PurchasesArray
[0] undefined
[1] { Student_Name: undefined }
[2] { Student_Name: 'Bob' }

以上内容在数组中均有效. [0]和[1]都会给您您收到的错误.

The above are all valid in an array. [0] and [1] will both give you the error you received.

如果PurchasesArray不是数组而是对象，那么您需要在循环内部进行检查.

If PurchasesArray is not an array but an object - then you need to do a check inside your loop.

for (var i in RewardPurchases.PurchasesArray) {
   if(!RewardPurchases.PurchasesArray.hasOwnProperty(i)) {
     continue;
   }

   //rest of code...
}

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