Summary of javaScript: Dom obtains collection element objects-JS Tutorial-php.cn

Summary of javaScript: Dom obtains collection element objects

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Release： 2022-08-05 16:21:42

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This article brings you relevant knowledge about javascript, which mainly introduces the related issues of DOM obtaining collection element objects. You can use for or for...of loop to iterate the elements in the collection. Element object to control its properties and methods. Let’s take a look at it. I hope it will be helpful to everyone.

Summary of javaScript: Dom obtains collection element objects

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Get the element object in the collection

Node collection is a collection of nodes (index starting from 0)

Use for or for...of loopIterate over the element objects in the collection to manipulate them Properties and methods.

Properties and methods	Simple description
length	Element objects in the node collection Number
[n] or item(n)	Returns the single element object corresponding to index n

//在if条件表达式中写出：orderCheckbox元素对象集合中的元素节点的个数大于0
if(orderCheckboxs.length>0) {
  // 使用普通的for循环迭代orderCheckboxs元素对象集合中的每个元素对象
  for(let i=0;i<orderCheckboxs.length;i++){
    // 在.前面用item(n)方式获取元素对象集合的元素对象。
    orderCheckboxs.item(i).checked= true;
    // 在.前面用[]方式获取元素对象集合的元素对象。
    orderCheckboxs[i].parentElement.className= &#39;item-selected&#39;;
  }

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//用一下箭头函数哈
selectAll.onchange= (e) => {
  // 下面的语句是循环体，使用for…of循环迭代orderCheckboxs元素对象集合，循环变量是ele
  for(let ele of orderCheckboxs){
      ele.checked= e.target.checked;
      if(e.target.checked) {
        ele.parentElement.classList.add('item-selected');
      } else {
        ele.parentElement.classList.remove('item-selected');
      }
  }
};

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It is generally recommended to use a for..of loop

***** Understand the following two methods of obtaining a collection of element objects.
document(or element).getElementsByClassName('class value')

Return the class in the descendants of the document fire element A collection of all element objects whose properties are parameters. The parameter can only be the value of the class attribute of the HTML element (that is, the class name).

document(or element).getElementsByTagName('tag name')

Return A collection of all element objects in the document or element's descendants with the tag named parameter. Parameters can only be the tag names of HTML elements.

const orders= document.getElementsByClassName('order');
const input= document.getElementsByTagName('input');

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Traverse nodes

will treat whitespace text nodes as child nodes, except parentNode. If not found, return null

Attribute	Description
parentNode	Returns the parent node of the current node
firstChild	Returns the first child node of the current node
lastChild	Returns the last child node of the current node
nextSibling	Returns the next sibling node of the current node
previousSibling	Returns the previous sibling node of the current node Sibling nodes

Code example:

<body>
<h1><a href="#">123</a></h1>
<h2>快捷支付</h2>
<div class="panel">
  <ul class="step">
    <li>开通</li>
    <li>下单</li>
  </ul>
</div>
<script>
const t= setInterval(() => {
    // 在赋值符右侧写出：通过遍历元素节点的方法获取curStep的上一个元素节点
    let lastStep=curStep.previousElementSibling ;
    // 在赋值符右侧写出：通过遍历元素节点的方法获取curStep的下一个元素节点
    let nextStep=curStep.nextElementSibling ;
</script>

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Traverse element nodes

The read-only nature of element objects,Only traverse element nodes (Ignore text and other nodes) , null if not found

<body>
<h1><a href="#">123</a></h1>
<h2>快捷支付</h2>
<div class="panel">
  <ul class="step">
    <li>开通</li>
    <li>下单</li>
  </ul>
</div>

<script>
(() => {
  const step= document.querySelector('.step');
  // 在赋值符右侧写出：通过遍历元素节点的方法获取class为step的第1个子元素节点。
  let curStep=step.firstElementChild;

  const t= setInterval(() => {
    // 在赋值符右侧写出：通过遍历元素节点的方法获取curStep的上一个元素节点
    let lastStep=curStep.previousElementSibling ;
    // 在赋值符右侧写出：通过遍历元素节点的方法获取curStep的下一个元素节点
    let nextStep=curStep.nextElementSibling ;
</script>

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Read-only attribute	Description
parentElement	Returns the parent element node of the element
firstElementChild	Returns the first child element node of the element
lastElementChild	Returns the last child element node of the element
nextElementSibling	Returns the next sibling element node of the element
previousElementSibling	Returns the previous sibling element node of the element

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javascript video tutorial、webfrontend】

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