How does the browser run javascript

With the rapid development of the Internet, JavaScript, as the main programming language for front-end development, has become an indispensable component. However, running JavaScript in a web page involves the browser processing the scripting language. So, this article will explore the process of how browsers run JavaScript.

1. Parsing of JavaScript programs

When the browser encounters the JavaScript code in the web page, it will be responsible for parsing the code and converting it into instructions that the computer can understand. This process is called It is the parsing of JavaScript programs. Parsing mainly includes the following steps:

1. Lexical analysis

The browser analyzes each word in the code and classifies them into a set of "tags", such as "if", "for", "var", etc. This process is called lexical analysis.

2. Syntax analysis

The browser combines all tags into a data structure similar to a syntax tree, making the program more structured. Here, the browser collects the structure of the entire program and builds the corresponding data structure. This process is called syntactic analysis.

3. Code optimization

The browser will optimize JavaScript code to improve its performance and execution efficiency. Code optimization includes optimization techniques such as removing unused code and variables.

4. Generate Bytecode

The parser generates an intermediate language called bytecode. These bytecodes are lightweight JavaScript files that are easier to process and execute by computers than source code. The generated bytecode is saved and will be executed later.

2. JavaScript execution process

1. Parser

In the browser, the JavaScript parser is responsible for parsing the code into bytecode module. The parser in the browser is affected by certain factors such as the parser's performance, hardware, browsing context, etc.

When the parser reads and converts the code, it stores the code in memory.

2. Memory

Once the code is converted into bytecode by the parser and stored in memory, the JavaScript engine can access it and execute the code.

3. Execution Context

When JavaScript code is executed, execution contexts are created and linked together. Execution context refers to the specific place where the current JavaScript code is executing, such as function calls, script execution, execution code blocks, etc. The execution context contains the environment (variables, functions, objects, etc.) in which the current code is executed, and they can be accessed through the scope chain. Additionally, execution contexts enter and exit the stack as code executes.

4. Execute JavaScript

When JavaScript code is executed, the bytecode is converted into machine code and executed in memory. At this point, the code can modify the value of the variable, add elements to the browser, send requests to the background, etc.

After the JavaScript code is executed, the execution results are returned to the browser, and the browser displays the results to the user.

3. JavaScript optimization techniques

Since parsing and executing JavaScript code requires time and computing resources, the process can be optimized through the following techniques:

1. Reduce Code volume and complexity

Avoid redundant code and unnecessary calculations, choose simpler and elegant solutions, reduce function calls, and use appropriate tools to manage code.

2. Use the latest JavaScript features

Updating your browser and using the latest JavaScript features can improve code performance and execution efficiency. Moreover, code quality and maintainability will be guaranteed.

3. Compress and cache JavaScript code

Uses compression and caching technology to compress JavaScript code into a file and store it in the cache, allowing it to load quickly and save pages Loading time.

4. Use tools to analyze code

Use tools to analyze JavaScript code, detect and eliminate potential problems, and improve the quality and readability of the code.

Summary:

This article introduces how the browser runs JavaScript code and how to optimize the process. Understanding how browsers convert JavaScript code into instructions that computers can understand is important for deepening your understanding of JavaScript, optimizing code, and improving execution efficiency.

The above is the detailed content of How does the browser run javascript. For more information, please follow other related articles on the PHP Chinese website!