javascript - 如何给所有 p 元素一个类名？

Question

我试图给我所有的 p 元素一个类名，似乎无法弄清楚这里的问题是什么。

var para = document.getElementsByTag("p");
para.className += "myClass";

Answer 1

您必须遍历集合并分配(它也是 document.getElementsByTagName("p");)

for (var i = 0; i < para.length; i++) {
    para[i].className += " myClass";
    //                   ^^^
    //As @nnnnnn pointed out - a space beforehand will ensure the class is added to existing classes - and not added as a single word.
}