Question

js 中出现这个个问题Cannot read property 'style' of undefined

<div class="ctrl">
<a href="#" class="ctrl-i" id="ctrl-2">
<img src="images/index.jpg">
</a><a href="#" class="ctrl-i" id="ctrl-2">
<img src="images/index.jpg">
</a><a href="#" class="ctrl-i" id="ctrl-2">
<img src="images/index.jpg"></a>
</div>

window.onload = function() {
my_change("ctrl-i");
}

function my_change(className) {
// 图形变换
var my_obj = document.getElementsByClassName(className);
for (var i = 0; i <= my_obj.length; i++) {
my_obj[i].onmouseover = function () {
// body... 鼠标经过
my_obj[i].style.backgroundColor = "#000";
}
}
}

Answer 1

window.onload = function () {
    my_change("ctrl-i");


    function my_change(className) {
        // 图形变换
        var my_obj = document.getElementsByClassName(className);
        for (var i = 0; i < my_obj.length; i++) {
            (function (index) {
                my_obj[index].onmouseover = function () {
                    // body...  鼠标经过
                    my_obj[i].style.backgroundColor = "#000";
                }
            })(i)
        }
    }
}

追问

这个是什么原理来着！！！index是哪里来的参数也没有定义呀！！