Uncaught TypeError: Cannot read property 'contains' of undefined

Question

您好，我喜欢遍历所有包含 class 活动的 "slide" 项，并获取它们的 "data-headertext" 属性。我做错了什么？

<div class="slide active"></div>

    var elems = document.getElementsByClassName('slide');

    for (var i = 0, len = elems.length; i < len; i++) {                
        if (elems.classList.contains("active")) {
          myJavascriptFunc
          }
        }

       function myJavascriptFunc() {
         alert(this.getAttribute('data-headertext'));
       }

Answer 1

elems 在你的代码中是一个没有属性 classList 的节点列表。您应该访问 elems

中元素的 classList

if (elems[i].classList.contains("active"))

更简单的方法：

也可以使用 querySelectorAll() giving it multiple classes and loop using forEach()

const elems = document.querySelectorAll('.slide.active')
elems.forEach(a => console.log(a.getAttribute('data-headertext')))

在这种情况下，您希望获得 data 属性。所以最好使用 HTMLElement.dataset `

const elems = document.querySelectorAll('.slide.active')
elems.forEach(a => console.log(a.dataset.headertext));

Uncaught TypeError: Cannot read property 'contains' of undefined

Uncaught TypeError: Cannot read property 'contains' of undefined

javascript

getattribute