[英]Shadow Root getElementsByClassName
I am using LitElement to create custom Web Components.我正在使用 LitElement 创建自定义 Web 组件。 I am fairly new at it and decided to try making image slideshow.
我对它相当陌生,并决定尝试制作图像幻灯片。 I used W3Schools slideshow as reference while modifying it to work as LitElement.
我使用W3Schools 幻灯片作为参考,同时修改它以用作 LitElement。 The problem is, that when I am trying to use document.getElementByClassName I am not getting anything.
问题是,当我尝试使用 document.getElementByClassName 时,我什么也没得到。 I am familiar with this issue since I am working with Shadow DOM so I changed it to this.shadowRoot.getElementsByClassName.
我很熟悉这个问题,因为我正在使用 Shadow DOM,所以我将其更改为 this.shadowRoot.getElementsByClassName。 Unfortunately, I get told that what I am trying to use is not a function.
不幸的是,我被告知我尝试使用的不是函数。 How Do I get elements by class name when I am working with LitElement and shadow dom?
当我使用 LitElement 和 shadow dom 时,如何按类名获取元素? In case you want to see how my component looks like, here is the code:
如果您想查看我的组件的外观,这里是代码:
import { LitElement, html} from '@polymer/lit-element';
class ImageGalleryElement extends LitElement {
static get properties() { return {
slideIndex: { type: Number },
}};
constructor(){
super();
this.slideIndex=1;
this.showSlides(this.slideIndex);
}
// Next/previous controls
plusSlides(n) {
this.showSlides(this.slideIndex += n);
}
// Thumbnail image controls
currentSlide(n) {
this.showSlides(this.slideIndex = n);
}
showSlides(n) {
var i;
console.dir(this.shadowRoot);
var slides = this.shadowRoot.getElementsByClassName("mySlides");
console.dir(slides);
var dots = this.shadowRoot.getElementsByClassName("dot");
if (n > slides.length) {this.slideIndex = 1}
if (n < 1) {this.slideIndex = slides.length}
for (i = 0; i < slides.length; i++) {
slides[i].style.display = "none";
}
for (i = 0; i < dots.length; i++) {
dots[i].className = dots[i].className.replace(" active", "");
}
slides[this.slideIndex-1].style.display = "block";
dots[this.slideIndex-1].className += " active";
}
render(){
return html`
<style>
* {box-sizing:border-box}
/* Slideshow container */
.slideshow-container {
max-width: 1000px;
position: relative;
margin: auto;
}
/* Hide the images by default */
.mySlides {
display: none;
}
/* Next & previous buttons */
.prev, .next {
cursor: pointer;
position: absolute;
top: 50%;
width: auto;
margin-top: -22px;
padding: 16px;
color: white;
font-weight: bold;
font-size: 18px;
transition: 0.6s ease;
border-radius: 0 3px 3px 0;
user-select: none;
}
/* Position the "next button" to the right */
.next {
right: 0;
border-radius: 3px 0 0 3px;
}
/* On hover, add a black background color with a little bit see-through */
.prev:hover, .next:hover {
background-color: rgba(0,0,0,0.8);
}
/* Caption text */
.text {
color: #f2f2f2;
font-size: 15px;
padding: 8px 12px;
position: absolute;
bottom: 8px;
width: 100%;
text-align: center;
}
/* Number text (1/3 etc) */
.numbertext {
color: #f2f2f2;
font-size: 12px;
padding: 8px 12px;
position: absolute;
top: 0;
}
/* The dots/bullets/indicators */
.dot {
cursor: pointer;
height: 15px;
width: 15px;
margin: 0 2px;
background-color: #bbb;
border-radius: 50%;
display: inline-block;
transition: background-color 0.6s ease;
}
.active, .dot:hover {
background-color: #717171;
}
/* Fading animation */
.fade {
-webkit-animation-name: fade;
-webkit-animation-duration: 1.5s;
animation-name: fade;
animation-duration: 1.5s;
}
@-webkit-keyframes fade {
from {opacity: .4}
to {opacity: 1}
}
@keyframes fade {
from {opacity: .4}
to {opacity: 1}
}
</style>
<!-- Slideshow container -->
<div class="slideshow-container">
<!-- Full-width images with number and caption text -->
<div class="mySlides fade">
<div class="numbertext">1 / 3</div>
<img src="../../img/img-snow-wide" style="width:100%">
<div class="text">Caption Text</div>
</div>
<div class="mySlides fade">
<div class="numbertext">2 / 3</div>
<img src="../../img/img-nature-wide" style="width:100%">
<div class="text">Caption Two</div>
</div>
<div class="mySlides fade">
<div class="numbertext">3 / 3</div>
<img src="../../img/img-mountains-wide" style="width:100%">
<div class="text">Caption Three</div>
</div>
<!-- Next and previous buttons -->
<a class="prev" @click="${this.plusSlides(-1)}" >❮</a>
<a class="next" @click="${this.plusSlides(1)}">❯</a>
</div>
<br>
<!-- The dots/circles -->
<div style="text-align:center">
<span class="dot" @click="${this.currentSlide(1)}"></span>
<span class="dot" @click="${this.currentSlide(2)}"></span>
<span class="dot" @click="${this.currentSlide(3)}"></span>
</div>
`;
}
}
// Register the element with the browser
customElements.define('image-gallery-element', ImageGalleryElement);
The getElementsByClassName()
method works only on a HTML Document or element. getElementsByClassName()
方法仅适用于 HTML 文档或元素。
The shadowRoot
is a Document Fragment by inheritance , not a Document nor a HTML element. shadowRoot
是继承的 Document Fragment ,而不是 Document 或 HTML 元素。
Instead you should use querySelectorAll()
.相反,您应该使用
querySelectorAll()
。
Update更新
It's the same behavior for:这是相同的行为:
getElementsByTagName()
getElementsByClassName()
Note 1注 1
getElementById()
is not available on (in memory) nodes created with document.createElement
getElementById()
在使用document.createElement
创建的(内存中)节点上不可用
Test Selector Methods: https://jsfiddle.net/CustomElementsExamples/bfge7mtj/测试选择器方法: https : //jsfiddle.net/CustomElementsExamples/bfge7mtj/
Note 2笔记2
Be aware slotted content is not moved to shadowDOM, it remains in ligthDOM请注意,开槽的内容不会移动到 shadowDOM 中,而是保留在 ligthDOM 中
When you move Elements from lightDOM (in main DOM) to shadowRoot,当您将元素从 lightDOM(在主 DOM 中)移动到 shadowRoot 时,
the Live Nodelist will be emptied实时节点列表将被清空
let pieces = document.getElementsByTagName("[TAGNAME here]");
console.warn(tags);// lists all tags
this.shadowRoot.append(...this.children);
console.warn(tags);// empty
LitElement also offers its own convenient decorators to access nodes: @query
, @queryAll
, and @queryAsync
decorators LitElement还提供了自己方便的装饰器来访问节点:
@query
、 @queryAll
和@queryAsync
装饰器
But for sure I understand if you want to stay vanilla :)但可以肯定的是,我理解你是否想保持香草味:)
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