How the web front-end works

With the development of the Internet, web front-end technology has become one of the widely used technologies. This article mainly introduces how the web front-end runs, including the writing of front-end code, code loading and execution, page rendering process, etc.

1. Writing of front-end code

Web front-end code is usually written in HTML, CSS, JavaScript and other languages. HTML is used to describe the structure of the page, CSS is responsible for the style of the page, and JavaScript is responsible for the interactive logic of the page. Code in these languages ​​can be written in various editors, such as Sublime Text, Visual Studio Code, etc.

2. Code loading and execution

The loading and execution of front-end code is an important part of running a web application. When a user accesses a web application, the browser first requests an HTML page. Once an HTML page is requested, the browser will request external files referenced in the page one by one according to the structure of the HTML, such as CSS, JavaScript and other files. These files are sent to the web server via so-called HTTP requests, and the web server responds to the browser request.

For JavaScript files, the browser will download it locally and run the code in it. During operation, JavaScript can operate elements on the page through the DOM API, and can also make asynchronous requests through technologies such as Ajax. At the same time, JavaScript can also use HTML5 Web Workers to improve execution efficiency.

3. Page rendering process

After the browser loads all HTML, CSS, and JavaScript files, the browser starts rendering the page. The browser's rendering process can usually be divided into the following steps:

1. Build a DOM tree: The browser will build a DOM tree based on the structure of the HTML file.

2. Style calculation: The browser will calculate which elements should apply which styles according to the rules of the CSS file.

3. Layout: The browser will calculate where each element should appear based on the size and position of the element.

4. Drawing: The browser will draw each element to the screen.

5. Composition: The browser will composite images of all elements on the screen and display them to the user interface.

4. Summary

This article mainly introduces how the web front-end runs, including the writing of front-end code, the loading and execution of code, the page rendering process, etc. For developers who develop web applications, it is very important to understand these basic principles, which can help them better develop efficient and high-quality web applications.

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