Explore the two main scenarios where JavaScript runs: browser and server-side

JavaScript is a scripting language that was originally used to implement some simple animation effects or interactive behaviors on web pages. Today, JavaScript can run both in the browser and on the server. This article will focus on the two main scenarios where JavaScript runs: the browser and the server side.

1. JavaScript runs in the browser

1.1 The process of the browser parsing JavaScript

JavaScript is the most widely used scripting language that runs in the browser. It can Works with HTML and CSS to achieve dynamic effects and interactive behaviors on web pages. When we open a web page that contains JavaScript in a browser, the browser automatically parses the JavaScript code and executes it.

Specifically, the process of browser parsing JavaScript is as follows:

1. The browser will first read the JavaScript code from the script tag of the web page;
2. The code is then compiled into bytecode (called scanning and parsing code);
3. The browser will convert the bytecode into machine code and execute it.

1.2 JavaScript environment in the browser

In the browser, JavaScript runs in an environment called the "JavaScript engine". Different browsers use different engines, the main ones are as follows:

• V8 engine: developed by Google, used in Chrome browser;
• SpiderMonkey engine: developed by Mozilla , used in Firefox browser;
• Trident engine: developed by Microsoft, used in Internet Explorer browser;
• Chakra engine: developed by Microsoft, used in Edge browser.

In addition to the basic operating environment, the browser also provides some DOM and BOM APIs for JavaScript to use, making it easier to operate web page elements and obtain browser environment information.

2. JavaScript runs on the server

2.1 Node.js

Node.js is a JavaScript running environment based on the Chrome V8 engine, which allows JavaScript to run on the server side . It provides an event-driven, non-blocking I/O programming model, allowing JavaScript to handle a large number of concurrent requests.

Node.js is widely used in web development, network applications, command line tools and other fields. It can access system files and network resources, and can also use third-party modules and libraries to make development work more efficient.

2.2 JavaScript and server

In the server, JavaScript mainly interacts with the client through the HTTP protocol. The main role of JavaScript is to complete data processing and communication logic on the server side. For example, when a user submits a form in a browser, the form data is sent to the server and parsed and processed via JavaScript.

In addition, JavaScript can also be used to establish a WebSocket connection to achieve real-time communication between the server and the client. This real-time communication technology is widely used in web chat, online games and other applications.

Summary

The application scenarios of JavaScript are not limited to the browser side, it is also receiving more and more attention on the server side. In the browser, JavaScript is mainly used to implement interactive effects and animations on web pages, while in the server, it is used to implement functions such as data processing and communication. With the help of Node.js and other tools, JavaScript can bring us more convenience and efficiency.

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