An in-depth analysis of the built-in modules in Node.js

This article will take you to understand the built-in modules inNode.js, take a look at the operating mechanism of Node.js built-in modules, and briefly introduce EventEmitter (observer mode) through examples.

Node.js architecture diagram

Built-in modules

Some chestnuts

• File SystemAPI for operating files
• ProcessRecord some information about the Node.js process
• OSOperating system related API
  • os.arch() Gets the architecture information of the operating system
  • os.cpus() Gets the operating system CPU and kernel related information

[Recommended learning: "nodejs Tutorial"]

Node.js built-in module operating mechanism

Through Node.js source code analysis

• The application layer code calls the Node.js module

• The Node.js module calls the underlying C module throughinternalBinding

  • The built-in modules of Node are stored in the lib folder

  • The built-in modules call theinternalBindingV8 level method

  • internalBindingIn the C code in the src directory, the

• C code defines some The underlying method is exported through the interface of V8 for the Node layer to call

• Finally, the Node layer returns to the application layer

EventEmitter(Observer mode)

In some cases, the data is not called through the Node.js source code, but directly notified to the Node.js code to do something through the underlying operating system, such as:EventEmitter

Chestnut

process.stdin.on("data", (e) => { const playerAction = e.toString().trim(); });

onThe principle of the event is to useClass: EventEmitter

EventEmitter can pass some changes that occur at the bottom layer, such as receiving a mouse event, to the application layer, so that developers can perform corresponding operations

Event listener application scenarios

Use Observer pattern to solve the problem of communication between multiple module objects

// index.js const EventEmitter = require("events").EventEmitter; class GeekTime extends EventEmitter { constructor() { super(); setInterval(() => { this.emit("newLesson", { price: Math.random() * 100 }); }, 3000); } } const geekTime = new GeekTime(); module.exports = geekTime;

// buy.js const geekTime = require("./index.js"); geekTime.addListener("newLesson", (res) => { console.log("有新课了!!", res.price); if (res.price < 80) { console.log("价格小于80,买买买！"); } });

• Node.js Chestnut:EventEmitter
• Browser Chestnut - addEventListener - removeEventListener

The difference between observer mode and publish-subscribe mode

Publish-subscribe mode, the registration and triggering of events occur on a third-party platform independent of both parties. JS implementation - callback function Observer pattern: Publishers will directly reach subscribers. JS implementation method - throwing events

You can refer toThis design pattern article-Nuggets booklet

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