What does javascript use to get dom elements?
Javascript method to get dom elements: 1. Use getElementById() to get the element based on the id; 2. Use getElementsByName() to get the element based on the name attribute; 3. Use getElementsByTagName() to get the element based on the tag name; 4. Use getElementsByClassName() to get elements based on the class name; 5. Use querySelector() to return the first element object based on the specified selector.
The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.
js consists of three parts:
ECMAScript: js syntax
DOM: Document Object Model
BOM: Browser Object Model
WebApi is a standard developed by the W3C organization. In WebApi we mainly Learning DOM and BOM is also a unique part of js for webapi. It is neither a unique category of js itself nor a part of js learning. However, before learning WebApi, you need the foundation of js as the basis of learning WebApi.
DOM
DOM Introduction: Document Object Model (DOM) is a standard programming interface recommended by the w3c group for processing extensible markup language (HTML or XML). w3c has defined a series of DOM interface, through which the content, structure and style of web pages can be changed.
Document: A page is a document. Document is used in DOM to represent
Element: All tags in the page are elements. In DOM Use element to represent
node: All content in a web page can be regarded as a node (labels, attributes, text, comments, etc.). Use node in DOM to represent
Get DOM elements
How to get elements
- Get based on id, use getElementById () method to get the object with the id element
<div>sj</div> <script> // 1、因为页面是从上往下执行的，所以先有标签，后来有script获取 // 2、get 获得 element 元素 by通过 --- 驼峰命名法 // 3、参数 id 是大小写敏感的 // 4、返回的是一个元素 var sj = document.getElementById('overview'); console.log(sj) // dir 打印我们返回的元素对象，更好的查看里面的属性和方法 console.dir(sj) </script>
Get based on the name attribute: Use the getElementsByName() method to return the specified The object collection of the name attribute
document.getElementsByName('name')
Get based on the tag name: Use the getElementsByTagName() method to return a collection of objects with the specified tag name.
<body>
<ul>
<li>花海</li>
<li>晴天</li>
<li>七里香</li>
<li>花海</li>
<li>晴天</li>
</ul>
<ul id="nav">
<li>花海2</li>
<li>晴天2</li>
<li>七里香2</li>
<li>花海2</li>
<li>晴天2</li>
</ul>
</body>
<script>
// 1、返回的是 获取过来元素对象的集合，以伪数组形式存储
var lis = document.getElementsByTagName("li");
console.log(lis);
// 获取特定的那个
console.log(lis[2]);
// 2、遍历元素对象
for(var i = 0; i < lis.length; i++) {
console.log(lis[i]);
}
// 3、element.getElementByTagName() 可以获取这个元素里面的某些标签
var nav = document.getElementById("nav");
var nav2 = nav.getElementsByTagName('li')
console.log(nav);
</script>
Note: Because what we get is a collection of objects, we need to traverse if we want to operate the elements. The element object obtained is dynamic
Acquired through the new method of HTML5
- getElementsByClassName('Type') Obtains elements according to the class name
// 1、使用 getElementByClassName 获取 class类名元素
var box = document.getElementsByClassName("box"); // 可以获取全部的 class名为 box的元素
console.log(box);- querySelector('selector') Returns the first element object based on the specified selector
// 2、querySelector 返回指定选择器的第一个元素对象 切记：里面选择器需要添加 .box #nav var firstBox = document.querySelector('.box') // 只能获取第一个class名为 box 的元素 console.log(firstBox); var nav = document.querySelector('#nav') console.log(nav); var li = document.querySelector('li') // 获取的也是第一个 li 元素 console.log(li);
- querySelectorAll('selector') Returns all the specified selectors Collection of element objects
// 3、querySelectorAll 返回 全部的 li 元素 var allBox = document.querySelectorAll('li') console.log(allBox);
Special element acquisition (body, html)
- Get body element
// 1. 获取 body 元素 var bodyEle = document.body; console.log(bodyEle)
- Get html elements
// 2. 获取 HTML 元素 var htmlEle = document.documentElement; console.log(htmlEle)
Note: The key point is to remember several ways to get ordinary elements. Body and html are not commonly used, just for understanding.
【Related recommendations: javascript video tutorial, Basic programming video】
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