


JavaScript study notes (19) Node operation implementation code_Basic knowledge
HTML example to be used in this section
- Project one
- Project two
- Project three
1. Create element node
The document.createElement() method is used to create elements. It accepts a parameter, which is the tag name of the element to be created, and returns the created element. Node
var div = document.createElement("div") ; //Create a div element
div.id = "myDiv"; //Set the div's id
div.className = "box"; //Set the div's class
After creating the element, you must add the element to the document tree
2. Add element node
The appendChild() method is used to add a node to the end of the childNodes list and return the element node to be added
var ul = document.getElementById("myList"); //Get ul
var li = document.createElement("li"); //Create li
li.innerHTML = "Item 4"; //Add text to li
ul.appendChild(li); / /Add li to the end of the ul child node
After adding:
- Project One
- Project Two
- Project Three
- Project Four
appendChild() method can also be added Elements that already exist will be moved from the original position to the new position
var ul = document.getElementById("myList"); //Get ul
ul.appendChild(ul.firstChild); //Move the first element node of ul to the end of the ul child node
After running (IE):
- Project Two
- Project Three
- Project One
insertBefore() method, if you do not insert the node at the end, but want to place it at a specific position, use this method, this method Accepts 2 parameters, the first is the node to be inserted, the second is the reference node, returns the element node to be added
var ul = document.getElementById("myList"); //Get ul
var li = document.createElement("li"); //Create li
li.innerHTML= "Item Four"; //Add text to li
ul.insertBefore(li,ul.firstChild); //Add li before the first child node of ul
After adding:
- Item four
- Item one
- Item two
- Project 3
var ul = document.getElementById("myList"); //Get ul
var li = document.createElement("li"); //Create li
li.innerHTML= "Item 4"; //Add text to li
ul.insertBefore(li,ul.null); //Add li to the end of the child node of ul
After adding:
- Item one
- Item two
- Item three
< ;li>Project 4
var ul = document.getElementById("myList"); //Get ul
var li = document.createElement("li"); //Create li
li.innerHTML= "Item 4"; //Add text to li
var lis = ul.getElementsByTagName("li") //Get the collection of all li's in ul
ul.insertBefore(li,lis[ 1]); //Add li before the second li node in ul
After adding:
- Project 1
- Item 4
- Item 2
- Item 3
removeChild() method, used to remove nodes, accepts a parameter, which is the node to be removed, and returns the removed node. Note that the removed node is still in the document , but its position is no longer in the document
ul.removeChild(lis[0]); //Remove the first li, Different from the above, you need to consider the differences between browsers
4. Replace element node
replaceChild() method, used to replace nodes, accepts two parameters, the first parameter is to insert node, the second one is the node to be replaced, return the replaced node
li.innerHTML= "Item Four"; //Add to li Text
var lis = ul.getElementsByTagName("li") //Get the collection of all li in ul
var returnNode = ul.replaceChild(li,lis[1]); //Replace the original with the created li The second li
5. Copy node
cloneNode() method, used to copy nodes, accepts a Boolean parameter, true means deep copy (copy the node and all its child nodes) , false means shallow copy (copy the node itself, do not copy the child nodes)
When operating nodes, please pay attention to the differences between IE and other browsers (discussed in Section 18)

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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