Javascript, as a scripting language, greatly simplifies our front-end development process. Among them, expressing the parent-child relationship is a very important concept. Let's briefly introduce how to express the parent-child relationship in Javascript.
1. DOM tree structure
Let’s first talk about the most widely used DOM tree structure in Javascript. The HTML DOM tree is a hierarchical structure in which each HTML element becomes part of a parent, child, or sibling relationship, and all nodes originate from a root. The nodes of the tree structure have the following concepts:
In the DOM tree, the element node is the closest point between the parent and child nodes. Common relationships. For example:
<div id="parent"> <ul> <li>item 1</li> <li>item 2</li> </ul> </div>
We can abstract a piece of HTML content into the above DOM structure, where the div
tag is the parent element of the ul
tag. The li
tag is a child element of the ul
tag and a grandson element of the div
tag. And how is this father-son relationship expressed in Javascript?
2. Node Object
In Javascript, we use Node objects to represent these DOM nodes. The Node object is a base class for all DOM nodes, and all DOM nodes inherit the properties and methods of Node. The Node object has the following common attributes:
parentNode
: indicates the parent node, and returns NULL if there is none. childNodes
: An array representing child nodes. previousSibling
: Represents the previous sibling node. nextSibling
: Indicates the next sibling node. Taking the above HTML code as an example, we can obtain the relationship between parent and child nodes in the following ways:
const div = document.getElementById('parent'); const ul = div.firstElementChild; const li1 = ul.firstElementChild; const li2 = li1.nextElementSibling; console.log(ul.parentNode === div); // true console.log(li1.parentNode === ul); // true console.log(li2.previousSibling === li1); // true console.log(li1.nextSibling === li2); // true
In the above code, we used getElementById
Method to get div
, and use the firstElementChild
method to get its first child element ul
. Next, we use the firstElementChild
method to get the first child element li1
of ul
, and the nextElementSibling
method to get li1 The last sibling node of
is li2
. Finally, we use the properties of the Node objects to detect the parent-child relationship between them.
3. Parent-child operations in jQuery
In addition to using Node objects to represent the relationship between parent-child nodes, jQuery also provides convenient DOM operation functions to achieve the same function. Here are some simple examples:
parent()
: This method returns the parent element of the matching element. You can pass in a selector to filter the results. $('li').parent() // 返回行成父子关系的ul节点
children()
: This method returns a collection of all child elements of the matching element collection. You can also pass in a selector to filter the results. $('div').children() // 返回div下的所有子元素
siblings()
: This method returns all sibling elements of the matching element. You can also pass in a selector to filter the results. $('li').siblings() // 返回li的兄弟元素(不包括它自己)
In the above simple example, jQuery provides a convenient method to help us find and operate the parent-child relationship of DOM nodes, simplifying the process of operating DOM nodes with Javascript.
Conclusion
Node objects are used in Javascript to represent the parent-child relationship of DOM nodes. When using Node objects, we can directly access the properties of the node, such as parentNode
, previousSibling
, etc. to obtain the relationship between parent and child nodes. In addition, the jQuery library also provides simpler and more convenient functions that allow us to operate and find the parent-child relationship between DOM nodes. By cleverly using these functions, we can greatly quickly complete the front-end development work and improve the efficiency of front-end development.
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