为什么我的数组中的某些值未定义 [英] Why are some values in my array undefined

问题描述

我在php中有一个for循环，在我的页面上添加了一些看起来像这样的复选框

I have a for loop in php that adds a number of checkboxes on my page that look like this

<input type="checkbox" name="checkbox[]">

我想用javascript来检查哪个被检查并在数组中添加值

I want to use javascript to check which is checked and add value in an Array

var cboxes = document.getElementsByName('checkbox[]');
var len = cboxes.length;
var imageArray = new Array();

for (var i = 0; i < len; i++) {
    if (cboxes[i].checked) {
        imageArray[i] = cboxes[i].value;
    } 
}

如果我有50个盒子并单击复选框号2 ，4和6，遍历我的数组，我得到结果。

If I have 50 boxes and click the checkbox number 2,4 and 6, loops through my array, I get the result.

for(var i = 0; i < imageArray.length; i++){
    gallery.innerHTML += imageArray[i] + "<br>";
}

-

undefined
Correct value
undefined
Correct value
undefined
Correct value

如果我检查数字1,2,3我得到结果

If I check number 1, 2, 3 I get the result

Correct value
Correct value
Correct value

为什么当我跳过复选框时，我得到了未定义的内容？我该如何解决？

Why do I get undefined when I skip a checkbox? How do I fix it

推荐答案

这是因为您要向数组中添加额外的元素。以此代码为例：

This is because you are adding extra elements to an array. Take this code, for instance:

var a = []; // empty array
a[1] = 'foo'; // don't set a[0]

console.log(a.length); // gives 2

Javascript将始终填写数组键列表中的空白。如果你错过了一些，Javascript将用 undefined 填写空白。

Javascript will always "fill in" gaps in the list of array keys. If you miss some out, Javascript will fill in the blanks with undefined.

而不是将元素添加到你的数组按键名称，只需将推送到数组的末尾：

Rather than adding the element to your array by the key name, just push it onto the end of the array:

imageArray.push(cboxes[i].value);

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