How to read javascript source code

JavaScript is an integral part of modern web development. If you want to be an excellent JavaScript developer, you not only need to master the basic knowledge of the language, but also need to have a deep understanding of the working principle of the JavaScript engine and the implementation mechanism of built-in functions.

Reading JavaScript source code is an important way to understand the inner workings of the JavaScript engine. In this article, we will introduce how to read and understand JavaScript source code.

1. Read official documentation

JavaScript is a standard written by ECMA (European Computer Manufacturers Association). The official documentation explains in detail the various syntaxes and APIs of the language, which is an important basis for reading the source code. The latest ECMAScript standard can be found on the ECMA International official website.

Before reading the source code, it is recommended to study these official documents and have an understanding of their content and language.

2. Learn the code base structure

Understanding the structure and architecture of the code base is an important prerequisite for reading source code. If you can understand the file organization and modularization mechanism within the code base, you will be able to understand the structure of the code more clearly, and thus better read and understand the source code.

Before reading the code base, it is recommended to be familiar with the directory structure of the code base and the relationship between code files. For example, the code repository for the V8 engine can be found on GitHub, which contains many subdirectories and files such as src, test, and tools. Not all of these subdirectories are part of the core code, so check carefully where the files are located and what they mean.

3. Learn the startup process

The startup process of the JavaScript engine is the key to understanding its internal mechanism. First, you need to know how JavaScript goes from input code to output results.

In the V8 engine, the execution process of JavaScript code starts from the command line, goes through a series of initialization and compilation processes, and finally outputs the result.

Specifically, it will first load a file or string containing JavaScript code, parse it into an abstract syntax tree (AST), then generate bytecode based on the AST, and then generate machine code, which is finally The underlying operating system executes. There is also a lot of optimizing and optimizing processes involved. If you understand this process, you can more clearly understand the entire engine and the implementation of its built-in functions.

4. Learn built-in functions

The built-in functions in JavaScript include many common functions, such as string operations, mathematical calculations, object operations, etc. If you want to understand the inner workings of the JavaScript engine, you need to have a deep understanding of how these functions are implemented.

Take the Math.max() function as an example. It is usually used to return the highest value among the parameters passed in. In the V8 engine, Math.max() is implemented by first traversing the input parameters, finding the largest value in the parameters, and then returning it. Understanding the implementation mechanism of built-in functions can help you better understand their usage and performance.

5. Learn debugging tools

Debugging tools are one of the important tools for reading and understanding JavaScript source code. Developers can use debugging tools to track and modify source code, evaluate code quality and performance, and discover errors and vulnerabilities in the code.

When learning debugging tools, you need to learn how to set and use breakpoints, single-step debugging, view stacks, view variable values, diagnose memory leaks and other functions. Common JavaScript debugging tools include Chrome developer tools, Node.js debugger, etc.

Conclusion

By learning the above points, you will be able to better understand the internal mechanism of the JavaScript engine and read and understand the source code more easily. Of course, when reading the source code, it is recommended to start with simple code and gradually delve into more complex code bases and built-in function implementations.

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