FOR 循环和字符串与 JavaScript 连接给我一个未定义的值
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FOR loop and string concatenating with JavaScript gives me an undefined value
提问by Morgan
I have the array
我有数组
var data = [name, address, city, country];
And the loop
和循环
var columns;
for (var i = 0; i < data.length; i++) {
columns += "data[" + i + "], ";
}
columns = columns.slice(0, -2);
alert(columns);
The alert message says
警报消息说
undefineddata[0], data[1], data[2], data[3]
What am I doing wrong here? I want to remove the undefined...
我在这里做错了什么？我想删除未定义的...
回答by Nick Craver
You need to startwith an empty string, like this:
您需要从一个空字符串开始，如下所示：
var columns = "";
Right now what you have is basically equivalent to:
现在你所拥有的基本上相当于：
var columns = undefined;
Which when concatenated to a string, gives you "undefined".
当连接到一个字符串时，会给你"undefined".
