具有未定义值的Javascript变量

Question

我有以下代码，但我不明白为什么answer变量的结果是＆＃34; 1234undefinedundefined＆＃34; 。不应该是＆＃34; 1234＆＃34; ？

https://jsfiddle.net/JSmithd/t5roheuL/

var theanswer = "1,2,3,4";
var answerarray = theanswer.split(",");
var answer = "";
alert(theanswer.length);
for (z = 0; z < theanswer.length - 1; z++) { 
    if (answerarray[z] != "," && answerarray[z] != "undefined") { 
        answer = answer + answerarray[z];
    }
}
alert(answer);

Answer 1

你的for循环语句中的编码错误。

for (z = 0; z < theanswer.length - 1; z++)

theanswer.length == 7

因为它是一个包含7个字符的字符串

这应该是

for (z = 0; z < answerarray.length; z++)

answerarray.length == 4

因为它的ARRAY有4个元素。进行拆分后，将其转换为数组。