1. Element node
//Test element node, output node name, node type, node value
var liElements=document.getElementsByTagName("li");
for(var i=0;i
alert(liElements[i].nodeType);
alert(liElements[i].nodeValue);
}
2. Attribute node
[/c//Test attribute node, output attribute node name, node type, node value
var liElements=document.getElementsByTagName("li");
for(var i=0;i
alert("attrElement.nodeName " attrElement.nodeName);
alert("attrElement.nodeType " attrElement. nodeType);
alert("attrElement.nodeValue " liElements[i].getAttribute("value"));
}ode]
3. Text node
[code]
//Test element node, output node name, node type, node value
var liElements=document.getElementsByTagName(" li");
for(var i=0;i
alert(liElements[i] .childNodes[0].nodeType);
alert(liElements[i].childNodes[0].nodeValue);
liElements[i].childNodes[0].nodeValue="Nanjing";
alert(liElements[i].childNodes[0].nodeValue);
//Another way to read Method
alert(liElements[i].firstChild.nodeName);
alert(liElements[i].firstChild.nodeType);
alert(liElements[i].firstChild.nodeValue);
}
4. Replace node
replaceChild()
Replaces a child node in a given parent element with another child node
var reference = element.replaceChild(newChild,oldChild);
The return value is a pointer to the The reference pointer of the child node being replaced.
If the inserted child node also has child nodes, those child nodes are also inserted into the target node
//Method 1
// var cityElement= document.getElementById("city");
// var loveElement=document.getElementById("love");
// var cityChildElement=document.getElementById("beijing");
// var loveChildElement =document.getElementById("fankong");
// var oldElement=cityElement.replaceChild(loveChildElement,cityChildElement);
// loveElement.appendChild(oldElement);
// alert(oldElement.getAttribute( "id"));
var cityElement=document.getElementById("city");
var cityElement.onclick=function(){
var cityChildElement=document.getElementById("beijing");
var loveChildElement=document.getElement ById ("fankong");
var oldElement=cityElement.replaceChild(loveChildElement,cityChildElement);
loveElement.appendChild(oldElement);
alert(oldElement.getAttribute("id"));
}
5. Find attribute nodes
getAttribute()
Returns the value of a given attribute node for a given element
var attributeValue = element.getAttribute(attributeName);
The name of the given attribute must be passed in the form of a string Give the method.
The value of the given attribute will be returned in the form of a string. If the given attribute does not exist, getAttribute() will return an empty string.
Get the attribute node through the attribute
getAttributeNode (name of the attribute) --Node
//Get the value of the attribute through the attribute name
var bjElement=document. getElementById("bj");
var attributeValue=eduElement.getAttribute("name");
alert("attributeValue " attributeValue);
//Get the node of the attribute through the attribute name
var bjNode=eduElement.getAttributeNode("name");
alert(eduNode.nodeValue);
alert(eduNode.nodeType);
alert(eduNode.nodeName);
6. Set attribute nodes
setAttribute()
Adds a new attribute value to a given element node or changes the value of its existing attribute.
element.setAttribute(attributeName,attributeValue);
The name and value of the attribute must be passed to this method in the form of a string
If this attribute already exists, its value will be refreshed;
If If it does not exist, the setAttribute() method will first create it and then assign a value to it.
//Get the reference of the element
var bjElement=document.getElementById("bj");
//Set the attribute value
bjElement.setAttribute("name","beijing");
//Get the set attribute value
var nameValue=bjElement.getAttribute("name");
alert("nameValue " nameValue);
7. Create new element nodes
createElement()
Creates a new element node according to the given tag name. The method has only one parameter: the name of the element to be created, which is a string.
var reference = document.createElement(element); The return value of the
method: is a reference pointer pointing to the newly created node. The return value is an element node, so its nodeType attribute value is equal to 1.
New element nodes will not be automatically added to the document. The new node has no nodeParent attribute. It is just an object that exists in the JavaScript context.
var pElement = document.createElement("p");
//Create a new element
var pElement=document.createElement("li");
//Set attribute value
pElement.setAttribute("id","pid");
//Get the parent element
var loveElement=document.getElementById("love");
//Add child elements to the parent element
loveElement.appendChild(pElement);
//Get the newly created element by id
var pidElement=document.getElementById("pid");
alert(pidElement.getAttribute("id"));
8. Create a new text node
createTextNode()
Creates a new text node containing the given text. The return value of this method is a reference pointer to the new text node.
var textNode = document.createTextNode(text); The
method has only one parameter: the text string contained in the new text node. The return value of the
method: is a reference pointer pointing to the new node. It is a text node, so its nodeType attribute is equal to 3.
New element nodes will not be automatically added to the document, and new nodes have no nodeParent attribute
var pElementText=document.createElement("li") ;
var textElement=document.createTextNode("Nanjing");
pElementText.appendChild(textElement);
9. Insert node (1)
appendChild()
Add a child node to the given element: the last child node of element . The return value of the
method is a reference pointer to the newly added child node.
This method is usually used in conjunction with createElement() createTextNode()
New nodes can be appended to any element in the document
var newliElement=document.createElement("li");
var textNode=document.createTextNode("Beijing");
newliElement.appendChild(textNode);
document.body. appendChild(newliElement);
var liElement=document.getElementsByTagName("li");
var textValue=liElement[0].firstChild.nodeValue;
alert(textValue);
10. Delete node
removeChild()
Removes a child node from a given element
var reference = element.removeChild(node);
The return value is a reference pointer to the deleted child node.
When a node is deleted by the removeChild() method, all child nodes contained in this node will be deleted at the same time.
- Beijing
var ulElement=document.getElementById("city");
var liElement=document.getElementById( "beijing");
ulElement.removeChild(liElement);
If you want to delete a node but don’t know which parent node it is, the parentNode attribute can help.
- Beijing
var liElement=document.getElementById("beijing");
var parentElement=liElement.parentNode;
parentElement.removeChild(liElement);
11. Traverse the node tree
ChildNodes: Returns an array consisting of the child nodes of a given element node:
var nodeList = node.childNodes;
Neither text nodes nor attribute nodes can contain any more child nodes, so they The ChildNodes property will always return an empty array.
If you want to know whether an element has child nodes, you can use the hasChildNodes method.
If you want to know how many child nodes a certain element has, you can use the length property of the childNodes array.
The childNodes attribute is a read-only attribute.
12. Get the first child node
firstChild: This attribute returns the first child node of a given element node and returns the pointer of this node object.
var reference = node.firstChild;
Neither text nodes nor attribute nodes may contain any child nodes, so their firstChild property will always return null.
The firstChild attribute of an element is equivalent to the first node in the childNodes node collection of this element, that is:
var reference = node.ChildNodes[0];
The firstChild attribute is a read-only attribute .
13. Get the last child node
lastChild: an attribute corresponding to firstChild.
nextSibling: Returns the next sibling node of a given node.
parentNode: Returns the parent node of a given node.
The node returned by the parentNode attribute is always an element node, because only element nodes may contain child nodes.
The document node has no parent node.
previousSibling: Returns the previous sibling node of a given node
14. innerHTML attribute
Almost all browsers support this attribute, but it is not part of the DOM standard.
The innerHTML attribute can be used to read and write the HTML content within a given element.
var divElement=document.getElementById("city");
divElement.innerHTML="

Yes, the engine core of JavaScript is written in C. 1) The C language provides efficient performance and underlying control, which is suitable for the development of JavaScript engine. 2) Taking the V8 engine as an example, its core is written in C, combining the efficiency and object-oriented characteristics of C. 3) The working principle of the JavaScript engine includes parsing, compiling and execution, and the C language plays a key role in these processes.

JavaScript is at the heart of modern websites because it enhances the interactivity and dynamicity of web pages. 1) It allows to change content without refreshing the page, 2) manipulate web pages through DOMAPI, 3) support complex interactive effects such as animation and drag-and-drop, 4) optimize performance and best practices to improve user experience.

C and JavaScript achieve interoperability through WebAssembly. 1) C code is compiled into WebAssembly module and introduced into JavaScript environment to enhance computing power. 2) In game development, C handles physics engines and graphics rendering, and JavaScript is responsible for game logic and user interface.

JavaScript is widely used in websites, mobile applications, desktop applications and server-side programming. 1) In website development, JavaScript operates DOM together with HTML and CSS to achieve dynamic effects and supports frameworks such as jQuery and React. 2) Through ReactNative and Ionic, JavaScript is used to develop cross-platform mobile applications. 3) The Electron framework enables JavaScript to build desktop applications. 4) Node.js allows JavaScript to run on the server side and supports high concurrent requests.

Python is more suitable for data science and automation, while JavaScript is more suitable for front-end and full-stack development. 1. Python performs well in data science and machine learning, using libraries such as NumPy and Pandas for data processing and modeling. 2. Python is concise and efficient in automation and scripting. 3. JavaScript is indispensable in front-end development and is used to build dynamic web pages and single-page applications. 4. JavaScript plays a role in back-end development through Node.js and supports full-stack development.

C and C play a vital role in the JavaScript engine, mainly used to implement interpreters and JIT compilers. 1) C is used to parse JavaScript source code and generate an abstract syntax tree. 2) C is responsible for generating and executing bytecode. 3) C implements the JIT compiler, optimizes and compiles hot-spot code at runtime, and significantly improves the execution efficiency of JavaScript.

JavaScript's application in the real world includes front-end and back-end development. 1) Display front-end applications by building a TODO list application, involving DOM operations and event processing. 2) Build RESTfulAPI through Node.js and Express to demonstrate back-end applications.

The main uses of JavaScript in web development include client interaction, form verification and asynchronous communication. 1) Dynamic content update and user interaction through DOM operations; 2) Client verification is carried out before the user submits data to improve the user experience; 3) Refreshless communication with the server is achieved through AJAX technology.


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