


The difference and connection between JavaScript and HTML DOM and the relationship between Javascript and DOM_javascript skills
Difference:
javascript
JavaScript is the most popular browser scripting language on the Internet. Very easy to use! You will love it!
JavaScript is used by millions of web pages to improve design, validate forms, detect browsers, create cookies, and more.
HTML DOM
HTML DOM is a W3C standard (the abbreviation of HTML Document Object Model, Document Object Model for HTML).
HTML DOM defines a standard set of objects for HTML, as well as standard methods for accessing and processing HTML documents.
Through the DOM, you can access all HTML elements, along with the text and attributes they contain. The content can be modified and deleted, and new elements can also be created.
HTML DOM is platform and programming language independent. It can be used by any programming language such as Java, JavaScript and VBScript.
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With JavaScript, you can reconstruct your entire HTML document. You can add, remove, change, or rearrange items on the page.
To change something on the page, JavaScript needs to gain access to all elements in the HTML document. This entry, along with the methods and properties for adding, moving, changing, or removing HTML elements, is obtained through the Document Object Model (DOM).
Javascript mainly uses HTML DOM to obtain, change, and create HTML elements, so as to achieve the goal of beautifying the page and operating the page elements. Therefore, the most common ones in Javascript are various HTML DOM elements and their respective attributes. In addition to these DOM elements, Javascript has its own objects, such as arrays.
To put it simply, Javascript can be considered to mainly manipulate the HTML DOM. The two are different.
Javascript is a language, and DOM is a model that can dynamically modify documents in various languages (not only js, but also php).
The relationship between JavaScript and DOM is separately pulled out below to explain in detail
JavaScript working with browsers
1. The browser fetches and loads your page and parses its content from top to bottom.
When encountering JavaScript, the browser parses the code, checks its correctness, and then executes the code.
The browser also creates an internal model (DOM) of the HTML page.
2. JavaScript continues to execute, using the DOM to inspect the page, complete modifications, accept events from the page, or ask the browser to obtain other data from the web server.
How does JavaScript interact with the page?
JavaScript is code, HTML is markup, completely different things
How to make them interact?
The answer is to use the Document Object Model (DOM).
The beauty of the DOM is that it provides a consistent way across all browsers to access the structure and content of HTML through code.
1. When the browser loads a page, the browser parses the HTML and creates an internal model of the document, which contains all elements of the HTML markup.
2. JavaScript can interact with DOM (JavaScript uses DOM to create or delete elements, etc.)
Document is an object that reflects HTML. By calling the document method, the state of the DOM is changed, that is, the HTML page is changed
3. When JavaScript modifies the DOM, the browser will dynamically update the page.
Homemade DOM
Materials: Correctly formatted HTML5 page, WEB browser
Method:
1. Create a document node at the top
2. Take the top-level element of the HTML page, here it is the element, and add it to the DOM as a child node of document
3. For each element nested in the current element, add the element to the DOM as a child node of the current element
4. For the newly added elements, perform the third step and repeat the work until all elements are processed
The HTML page is as follows
<!DOCTYPE html> <html lang="helloworld"> <head> <title>DOM</title> <meta cherset="utf-"> <script src="dom.js" ></script> </head> <body> <h>My Dom</h> <div id="entry"> <h>hello</h> <p> Today, I am making a dom!!! </p> </div> </body> </html>
The obtained DOM is as shown below

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.

Understanding how JavaScript engine works internally is important to developers because it helps write more efficient code and understand performance bottlenecks and optimization strategies. 1) The engine's workflow includes three stages: parsing, compiling and execution; 2) During the execution process, the engine will perform dynamic optimization, such as inline cache and hidden classes; 3) Best practices include avoiding global variables, optimizing loops, using const and lets, and avoiding excessive use of closures.

Python is more suitable for beginners, with a smooth learning curve and concise syntax; JavaScript is suitable for front-end development, with a steep learning curve and flexible syntax. 1. Python syntax is intuitive and suitable for data science and back-end development. 2. JavaScript is flexible and widely used in front-end and server-side programming.

Python and JavaScript have their own advantages and disadvantages in terms of community, libraries and resources. 1) The Python community is friendly and suitable for beginners, but the front-end development resources are not as rich as JavaScript. 2) Python is powerful in data science and machine learning libraries, while JavaScript is better in front-end development libraries and frameworks. 3) Both have rich learning resources, but Python is suitable for starting with official documents, while JavaScript is better with MDNWebDocs. The choice should be based on project needs and personal interests.

The shift from C/C to JavaScript requires adapting to dynamic typing, garbage collection and asynchronous programming. 1) C/C is a statically typed language that requires manual memory management, while JavaScript is dynamically typed and garbage collection is automatically processed. 2) C/C needs to be compiled into machine code, while JavaScript is an interpreted language. 3) JavaScript introduces concepts such as closures, prototype chains and Promise, which enhances flexibility and asynchronous programming capabilities.

Different JavaScript engines have different effects when parsing and executing JavaScript code, because the implementation principles and optimization strategies of each engine differ. 1. Lexical analysis: convert source code into lexical unit. 2. Grammar analysis: Generate an abstract syntax tree. 3. Optimization and compilation: Generate machine code through the JIT compiler. 4. Execute: Run the machine code. V8 engine optimizes through instant compilation and hidden class, SpiderMonkey uses a type inference system, resulting in different performance performance on the same code.

JavaScript's applications in the real world include server-side programming, mobile application development and Internet of Things control: 1. Server-side programming is realized through Node.js, suitable for high concurrent request processing. 2. Mobile application development is carried out through ReactNative and supports cross-platform deployment. 3. Used for IoT device control through Johnny-Five library, suitable for hardware interaction.


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