这个错误是为什么啊？

Question

目的是想让二级菜单下的图片做一个margin-left的缩入

script标签页放在body之后的，报错是
Uncaught TypeError: Cannot read property 'classList' of undefined
at HTMLButtonElement.btnaaaaaaa.onclick

btnaaaaaa这个按钮是加上去测试的。。。

Answer 1

闭包问题，你把k打印出来就知道了，你的k始终为lan，rotatGroup[lan]肯定是undefinedfor (var k=0;k<lan;k++){&nbsp; &nbsp; (function(k){&nbsp; &nbsp; &nbsp; &nbsp; btnaaaaaa.onclick = function(){&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; rotatGroup[k].classList.toggle('rotate')&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; })(k)};你的意图可能是：&nbsp; &nbsp; btnaaaaaa.onclick = function(){&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;for (var k=0;k<lan;k++){&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; rotatGroup[k].classList.toggle('rotate');&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp;}