How nodejs is executed

Node.js is an open source JavaScript runtime environment that allows developers to use JavaScript to write server-side code, as well as run command line tools, web crawlers, etc. This article will introduce the execution process of Node.js.

1. Execution architecture of Node.js

Node.js is built on the V8 engine, which is a famous open source JavaScript engine originally developed by Google. It can compile JavaScript code into machine-readable machine code and achieve high-performance operation. Node.js also adds some built-in modules based on V8, such as file system (fs), HTTP and other modules. These modules are written in C, which can speed up code execution efficiency.

2. The execution process of Node.js

The execution process of Node.js can be divided into the following stages:

1. Parse the script file

When Node.js reads a JavaScript file, it first parses the file. The parsing process mainly includes two links: lexical analysis and syntax analysis.

Lexical analysis: Extract words and symbols (tokens) from files. Words refer to keywords, identifiers, literals, etc. in JavaScript. Symbols refer to operators, semicolons, parentheses, etc. Extracting and classifying these words and symbols is the core work of lexical analysis.

Grammatical analysis: Convert a sequence of words and symbols into sentences. This is grammatical analysis. The core of syntax analysis is the construction of a syntax tree, which is a tree representation of an abstract syntax structure. It represents statements and expressions in the form of nodes, and connections are established between nodes through parent-child relationships. After the syntax tree is constructed, you can proceed to the next step.

2. After the parsing is completed, execute the JavaScript code

After the parsing is completed, Node.js will execute the JavaScript code according to the parsed syntax tree. With the help of the V8 engine, JavaScript code will be compiled into machine code. This process will only happen once during the first run. Subsequent executions will directly use the previously compiled machine code. This is also the advantage of the V8 engine.

3. Convert JavaScript code into bytecode

In order to further improve execution efficiency, Node.js will convert JavaScript code into bytecode before executing JavaScript code. . Because bytecode is closer to machine code than source code, execution efficiency is higher, and there is no need to start parsing from source code again.

4. Node.js event loop mechanism

In addition to the above process, Node.js also has a very important mechanism, which is the event loop mechanism. The event loop is the core mechanism for performing I/O operations in Node.js and is also the cornerstone of asynchronous programming. The core idea of ​​the event loop is that when an event occurs, the program will call the corresponding callback function to handle the event.

The event loop mechanism can be divided into the following steps:

1. Add asynchronous tasks to the event queue
2. Execute synchronous tasks
3. From the queue Take out the asynchronous task and execute its callback function
4. Go back to the second step

It can be seen that when Node.js executes JavaScript code, it does not proceed in a linear sequence, but in a linear order. Asynchronous operations are implemented through the event loop mechanism, which is also the advantage of Node.js.

5. Summary

Node.js is a very excellent JavaScript runtime environment. Its execution process is very clear: parse script files, execute JavaScript code, and convert JavaScript code into Bytecode, and Node.js also has a very important event loop mechanism that can implement non-blocking I/O operations. I believe that as Node.js continues to develop, it will play an increasingly important role in web development.

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