javascript＆＃34;无法阅读财产＆＃39;已检查＆＃39; of null＆＃34;

Question

function piliang() {
    var ids = "";
    var num = document.getElementsByName("check");
    for (var i = 0; 1 < num.length; i++) {
        if (num.item(i).checked) {
            ids = ids + num.item(i).value + ",";
        }
        alert(ids);
    }

成功运行

function piliang() {
    var ids = "";
    var num = document.getElementsByName("check");
    for (var i = 0; 1 < num.length; i++) {
        if (num.item(i).checked) {
            ids = ids + num.item(i).value + ",";
        }
    }

这会发出以下错误：

  

＆＃34;无法阅读财产＆＃39;已检查＆＃39; of null＆＃34;

第一个代码也有此错误，但可以成功运行

我的英语不好，请尝试用代码解释一下，非常感谢

Answer 1

修正了for循环

function piliang() {
    var ids = "";
    var num = document.getElementsByName("check");
    for (var i = 0; 1 < num.length; i++) {    //use i instead of 1
        if (num.item(i).checked) {
            ids = ids + num.item(i).value + ",";
        }
    }