为什么我收到此错误？Uncaught TypeError：无法读取未定义的属性“ length”
[英]why I am getting this error Uncaught TypeError: Cannot read property 'length' of undefined
问题描述
I want sort this sentence "This account has an unconfirmed email address" by word length how can i do this. 
我想按字长对“该帐户的电子邮件地址未经确认”这句话进行排序，我该怎么做。
<script>
$(document).ready(function(){
var some = "";
xx = "";
var vText = "This account has an unconfirmed email address";
slitTxt = vText.split(" ");
for(i=0; i <= slitTxt.length; i++ ){
xx = slitTxt[i].length;
some = $('body').append(xx+" ")
}
});
</script>
3 个解决方案
解决方案1
1 已采纳 2014-12-08 16:12:24
you are checking for lastindex+1 that does'nt exist or is undefined, remove equals to sign from loop condition replace "<=" with "<" 您正在检查不存在或未定义的lastindex + 1，请从循环条件中删除等于符号以将“ <=”替换为“ <”
for example if array length is 5 using <= array.length means that check for 5 or less than 5 ,here first index is 0 and last is 4 so 5 is undefined 例如，如果使用<= array.length的数组长度为5，则表示检查5或小于5，这里第一个索引为0，最后一个索引为4，所以5是未定义的
<script>
$(document).ready(function(){
var some = "";
xx = "";
var vText = "This account has an unconfirmed email address";
slitTxt = vText.split(" ");
for(i=0; i < slitTxt.length; i++ ){
xx = slitTxt[i].length;
some = $('body').append(xx+" ")
}
});
</script>
解决方案2
1 2014-12-08 16:13:48
The error come because of this line : 由于此行而导致错误：
for(i=0; i <= slitTxt.length; i++ )
An array is 0-indexed, which mean the first cell is 0 but the length would be 1 数组的索引为0，这意味着第一个单元格为0但长度为1
So if you array contain 5 elements, the last one will be arr[4] or arr[arr.length-1] 因此，如果数组包含5个元素，则最后一个将是arr[4]或arr[arr.length-1]
So when your condition in the for loop is i <= slitTxt.length , the last iteration will be the same as slitTxt[slitTxt.length] , hence, it will be undefined . 因此，当您在for循环中的条件是i <= slitTxt.length ，最后一次迭代将与slitTxt[slitTxt.length]相同，因此它将是undefined 。
Try that instead : 尝试尝试：
for(i=0; i < slitTxt.length; i++ )
解决方案3
0 2014-12-08 16:19:13
You can use map() instead of for loop. 您可以使用map()代替for循环。 Example: 例：
var vText = "This account has an unconfirmed email address", slitTxt = vText.split(" "); slitTxt.map(function(val, ind){$('body').append(val + " ");});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.9.0/jquery.min.js"></script> <html><body></body></html>
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