Web Front-endJS TutorialAccess, create, modify, and delete DOM nodes in JavaScript_Basic knowledgeAccess, create, modify, and delete DOM nodes in JavaScript_Basic knowledge
DOM
DOM is the abbreviation of Document object Model. The document object model is a document that expresses XML or HTML in the form of tree nodes. Using DOM methods and properties, you can access, modify, delete any element on the page, and you can also add an element. DOM is a language-independent API that can be implemented in any language, including Javascript
Take a look at one of the texts below.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html> <head> <title>My page</title> </head> <body> <p class="opener">first paragraph</p> <p><em>second</em> paragraph</p> <p id="closer">final</p> </body> </html>
Let’s take a look at the second paragraph
<p><em>second</em> paragraph</p>
You can see that this is a p tag. It is included in the body tag. So body is the parent node of p, and p is the child node. The first and third paragraphs are also child nodes of the body. They are all sibling nodes of the second paragraph. This em tag is a child node of the second segment p. Therefore p is its parent node. The parent-child node relationship can depict a tree-like relationship. So it’s called DOM tree.
Core DOM and HTML DOM
We already know that DOM can depict HTML and XML documents. In fact, an HTML document is an XML document, but more standardized. Therefore, as part of DOM Level 1, the Core DOM specification applies to all XML documents and the HTML DOM specification extends Core DOM. Of course, HTML DOM does not apply to all XML documents, only to HTML documents. Let’s take a look at the constructors of Core DOM and HTML DOM.
Constructor relationship
Access DOM node
Before validating the form or changing the image, we need to know how to access the element (element.). There are many ways to get elements.
Document node
We can access the current document through document. We can use firebugs (Firefox plug-in) to view the document's properties and methods.
All nodes have nodeType, nodeName, nodeValue attributes. Let’s take a look at the nodeType of document
document.nodeType;//9
There are 12 node types in total. document is 9. Commonly used ones are element (element: 1), attribute (attribute: 2), and text (text: 3).
Nodes also have names. for HTML tags. The node name is the label name. The name of the text node (text) is #text. The name of the document node (document) is #document.
Nodes also have values. For text nodes, the value is the text. The value of document is null
documentElement
XML will have a ROOT node to wrap the document. for HTML documents. The ROOT node is the html tag. Access the root node. You can use the properties of documentElement.
document.documentElement;//<html> document.documentElement.nodeType;//1 document.documentElement.nodeName;//HTML document.documentElement.tagName;//对于element，nodeName和tagName相同
Child Nodes
In order to determine whether it contains child nodes, we can use the following method
document.documentElement.hasChildNodes();//true
HTML has two child nodes.
document.documentElement.childNodes.length;//2 document.documentElement.childNodes[0];//<head> document.documentElement.childNodes[1];//<body>
You can also access the parent node through the child node
document.documentElement.childNodes[1].parentNode;//<html>
We assign the reference of body to the variable
var bd = document.documentElement.childNodes[1]; bd.childNodes.length;//9
Let’s look at the structure of the body
<body> <p class="opener">first paragraph</p> <p><em>second</em> paragraph</p> <p id="closer">final</p> <!-- and that's about it --> </body>
Why is the number of child nodes 9?
First there are 4 P’s and a comment, a total of 4.
4 nodes include 3 blank nodes. That’s 7.
The 8th blank node between body and first p.
The ninth one is the blank node between the comment and
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