setAttribute不是函数

Question

这里是html

<ul>
    <li>lorem</li>
    <li>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Eaque magnam expedita aspernatur suscipit ea ad nisi corporis sequi labore consequatur odit, impedit quia quisquam inventore, recusandae similique esse excepturi distinctio.</li>
    <li>Susan</li>
    <li>Lorem ipsum dolor sit amet consectetur adipisicing elit. Ad vitae consequatur vel nostrum? Sunt, quas iure libero aut laborum facere unde quidem dolorem dicta, eaque, eveniet dolore harum iste deleniti.</li>
</ul>

和js

var text = document.getElementsByTagName('ul')[0];

var firstItem = text.firstChild;

var lastItem = text.lastChild;

firstItem[0].setAttribute('class', 'complete');

浏览器显示错误，例如：

firstItem.setAttribute不是函数

Answer 1

您需要执行firstItem.setAttribute('class', 'complete');，因为firstItem中已经包含一个元素。