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Dom node vs element, what is the difference between the two?

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2021-05-20 10:34:422885browse

Dom node vs element, what is the difference between the two?

Document Object Model (DOM) is an interface that treats HTML or XML documents as a tree structure, in which each Each node is an object of the document. DOM also provides a set of methods to query the tree, change structure, and style.

DOM also uses the term element (Element) which is very similar to a node. So, what is the difference between DOM nodes and elements?

1. DOM nodes

The key to understanding the difference between nodes and elements is to understand what a node is.

From a higher perspective, a DOM document consists of a node hierarchy. Each node can have parents and/or children.

Look at the following HTML document:

<!DOCTYPE html>
<html>
  <head>
    <title>My Page</title>
  </head>
  <body>
    <!-- Page Body -->
    <h2>My Page</h2>
    <p id="content">Thank you for visiting my web page!</p>
  </body>
</html>

The document contains the following node hierarchy:

Dom node vs element, what is the difference between the two?

## is a node in the document tree. It has 2 child nodes:

and .

A node with 3 child nodes: Comment node , Title, paragraph

. The parent node of the

node is the node. The tag in the HTML document represents a node. Interestingly, ordinary text is also a node. Paragraph node

has 1 child node: text node "Thank you for visiting my web page!".

1.2 Node Type

How do we distinguish these different types of nodes? The answer lies in the DOM Node interface, specifically the

Node.nodeType attribute.

Node.nodeType can have one of the following values ​​representing the node type:

    Node.ELEMENT_NODE
  • Node.ATTRIBUTE_NODE
    • Node.TEXT_NODE
  • Node.CDATA_SECTION_NODE
  • Node.PROCESSING_INSTRUCTION_NODE
  • Node.COMMENT_NODE
  • Node.DOCUMENT_NODE
  • Node. DOCUMENT_TYPE_NODE
  • Node.DOCUMENT_FRAGMENT_NODE
  • Node.NOTATION_NODE
constants meaningfully indicate node types: for example

Node.ELEMENT_NODE represents element nodes, Node.TEXT_NODE represents the text node, Node.DOCUMENT_NODE the document node, and so on.

For example, let us select the paragraph node and view its

nodeType attribute: 

const paragraph = document.querySelector(&#39;p&#39;);

paragraph.nodeType === Node.ELEMENT_NODE; // => true

The node type that represents the entire node document tree is

Node.DOCUMENT_NODE：

document.nodeType === Node.DOCUMENT_NODE; // => true

2. DOM elements

After mastering the knowledge of DOM nodes, it is now time to distinguish between DOM nodes and elements.

If you understand node terminology, the answer is obvious: elements are nodes of a specific type

element (Node.ELEMENT_NODE), as well as types such as document, comment, text, etc.

In short, elements are nodes written using markup in an HTML document.

,

, <code>, </code> ,

,

are all elements because they are represented by tags.

Document type, comment, text nodes are not elements because they are not written using tags:

Node is the constructor of the node, HTMLElement is Constructor for elements in JS DOM. A paragraph is both a node and an element, it is an instance of both Node and HTMLElement

const paragraph = document.querySelector(&#39;p&#39;);

paragraph instanceof Node;        // => true
paragraph instanceof HTMLElement; // => true

Simply put, elements are subtypes of nodes, just like cats are animals The subtypes are the same.

3. DOM attributes: nodes and elements

In addition to distinguishing between nodes and elements, it is also necessary to distinguish between DOM attributes that contain only nodes or only elements.

The following properties of the node type evaluate to a node or collection of nodes (

NodeList): 

node.parentNode; // Node or null

node.firstChild; // Node or null
node.lastChild;  // Node or null

node.childNodes; // NodeList

However, the following properties evaluate to an element or collection of elements (

HTMLCollection): 

node.parentElement; // HTMLElement or null

node.children;      // HTMLCollection

Since both

node.childNodes and node.children return a list of children, why do you have both properties? good question!

Consider the following paragraph element that contains some text: 

<p>
  <b>Thank you</b> for visiting my web page!
</p>

Open the

demo and look at the childNodes and children# of the paragraph node ##Properties: <pre class="brush:js;toolbar:false;">const paragraph = document.querySelector(&amp;#39;p&amp;#39;); paragraph.childNodes; // NodeList: [HTMLElement, Text] paragraph.children; // HTMLCollection: [HTMLElement]</pre>

paragraph.childNodes

The collection contains 2 nodes: <b>Thank you</b>, and for visiting my web page!Text node! However, the

paragraph.children

collection contains only 1 item: <b>Thank you</b>. Since

paragraph.children

only contains elements, the text node is not included here because its type is text (Node.TEXT_NODE), not element (Node.ELEMENT_NODE). <p>Having both <code>node.childNodes and node.children, we can choose the set of children to access: all child nodes or only children that are elements.

4. Summary

A DOM document is a hierarchical collection of nodes, each node can have parents and/or children. Understanding the difference between DOM nodes and elements is easy if you understand what nodes are.

Nodes have types, and element types are one of them. Elements are represented by tags in HTML documents.

English original address: https://dmitripautin.com/dom-node-element/

Author: Shadeed

Source: dmitripavlutin

For more programming-related knowledge, please visit: Programming Teaching! !

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