How does browser javascript

How does the browser javascript

Javascript is a scripting language commonly used in front-end web development. As a carrier for running JavaScript, the browser is one of the most widely used environments. In this article, we'll take a closer look at how browsers run javascript.

1. The main functions of the browser

Before discussing how the browser runs javascript, we first need to understand the main functions of the browser. A browser is a software used to access the Internet. Its main functions include:

1) Make a request to the server to obtain resources such as pages;

2) Transfer the obtained resources such as pages Parse into a readable format;

3) Present the parsed content to the user.

2. The javascript engine in the browser

The javascript engine in the browser is a program that executes javascript code. It is responsible for reading and interpreting JavaScript code and converting it into executable instructions. Different browsers use different javascript engines.

The most popular JavaScript engine at present is Google's V8 engine. The V8 engine was developed by Google and was originally designed for the Google Chrome browser. Over time, V8 engines were used in more and more applications.

3. Execution process of javascript code

The execution process of javascript code can be divided into the following steps:

1) Analysis: The browser will first Parse the JavaScript code in the web page and convert it into executable instructions. During the parsing process, issues such as grammatical errors are checked.

2) Compilation: The browser compiles the parsed javascript code into machine code so that the computer can execute them. Most browsers use Just-In-Time Compilation (JIT) to compile and optimize code in real time when the code is executed.

3) Execution: The browser starts executing the javascript code and performs different operations according to the instructions in the code. During execution, the JavaScript engine will allocate and manage memory based on the variables in the JavaScript code.

Since javascript is single-threaded, the execution of javascript code is performed in sequence. This means that while the JavaScript code is executing, other features of the browser (such as the user interface, etc.) stop responding.

4. javascript running environment

The javascript running environment refers to the environment in which javascript code can run. In addition to browsers, javascript code can also run in the following environments:

1) Server: javascript code can run on the server side through Node.js.

2) Desktop applications: Some desktop applications (such as Electron) use javascript to write applications.

3) Mobile applications: Some mobile applications (such as React Native) use javascript to write the application.

5. Summary

Javascript is a widely used scripting language that plays an important role in front-end web development. As one of the main running environments for JavaScript, the browser realizes the parsing, compilation and execution of JavaScript code through the JavaScript engine. Familiarity with the JavaScript running process and JavaScript running environment can help developers better understand and optimize the code.

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