01. Node. Js

Node.js is a JavaScript runtime environment based on the Chrome V8 engine

Installation and operation

Nodejs.org/zh-cn/downl…

Create a project

mkdir node
cd node
npm init -y
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Create a new index.js file

All this code does is output the contents of the package.json file.

Version management

How to Switch Node.js versions on the same device Version management tool:

  • N: an NPM global open source package, is a dependencynpm To global installation, use
  • FNM: Fast, simple and compatible.node-version 和.nvmrcfile
  • NVM: standalone package,Node Version Manager

The characteristics of

Asynchronous I/O, single thread, cross-platform

Asynchronous I/O

When Node.js performs an I/O operation, the response returns and the operation resumes, rather than blocking the thread and wasting CPU loops waiting.

When Node.js performs an I/O operation, the response returns and the operation resumes, rather than blocking the thread and wasting CPU loops waiting

* The order in which code is written has nothing to do with the order in which it is executed

const { readFile } = require('fs');

readFile('./package.json', { encoding: 'utf-8' }, (err, data) => {
    if (err) {
        throw err;
    }
    console.log(data);
});
console.log(123456);
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Single thread

Node.js preserves the single-threaded nature of JavaScript in the browser

Advantages:

  • You don’t have to worry about state synchronization everywhere, deadlocks don’t happen
  • There is no performance overhead associated with thread context switching

Disadvantages:

  • Unable to utilize multi-core CPUS
  • Errors can cause the entire application to quit, resulting in poor robustness
  • A large number of calculations occupy the CPU and cannot be performed

Take the browser as an example. The browser is multi-process and the JS engine is single-thread

Browser process: The main Browser process, only one

Plug-in process: Created when the plug-in is used

GPU process: at most one is used for 3D drawing

Rendering process: page rendering, JS execution, event processing

  • GUI rendering thread +
  • JS engine thread + V8
  • Event trigger thread
  • Timer trigger thread
  • An asynchronous request

cross-platform

Compatible with Windows and Linux platforms, mainly due to the construction of a layer of platform architecture between the operating system and Node upper module system.

Application scenarios

Node.js has its place in most areas, especially I/O intensive ones

  1. Web applications: Express/Koa
  2. Front-end build: Webpack
  3. GUI client software: VSCode/netease Cloud Music
  4. Others: real-time communication, crawler, CLI, etc

02. Modularity mechanism

1. What is modularity?

To break a large program into smaller interdependent files based on function or business and then assemble them in a simple way

2. Why modular? No modularity problem

  • All script tags must be in the correct order, otherwise they will rely on errors
  • Global variables have name conflicts and cannot be reclaimed
  • IIFE/namespace can cause a lot of problems with code readability

Common. JS specification

Node.js supports the CommonJS module specification and loads modules synchronously

Loading mode:

  1. Load the built-in module require(‘fs’)
  2. Load relative | absolute path to the file module
  • require('/User/... /file.js')Copy the code
  • require('./file.js')
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  1. Load NPM package require(‘lodash’)

NPM: require(‘lodash’)

  1. Current directory node_modules
  2. If not, ndoe_modules of the parent directory
  3. If not, recurse up the path to node_modules in the root directory
  4. If package.json.main is not found, the file will be loaded. If package.json is not found, the file will be searched for index.js, index.json, and index.node in sequence

Require. The cache contains loaded modules. The reason for the cache is synchronous loading

  1. File module search time, if every require needs to search again, the performance will be more check;
  2. In real development, modules may contain side effect code

Other modular specifications

  • AMD is RequireJS in the promotion process of standardized output, asynchronous loading, advocate dependency preloading;
  • CMD is the standardized output of SeaJS in the promotion process, asynchronous loading, advocating the nearest dependence;
  • The UMD specification is compatible with AMD and CommonJS schemas
  • ES Modules(ESM), a language-level modularity specification that is context-independent and compiled with Babel

ES Modules(ESM)

ESM is a modular standard proposed in ES6 language level. The ESM contains two keywords: import and export. Console. log cannot print two keywords.

CommonJS VS ESM

  • The CommonJS module prints a copy of the value; The ESM module outputs references to values
  • CommonJS modules are loaded at runtime; ESM modules are compile-time output (pre-loaded)

Can mix, but it is not recommended (import commonjs | | the require of imprt)

2.6 Common Modules

03. Package management

Introduce NPM

NPM is package management in Node.js and provides install, delete, and other commands to manage packages

Private NPM

  • Mirror company internal private NPM
  • NPM config set registry=bnpm.byted.org

other

  • The parallel installation
  • Flat management
  • Lockfile
  • Cache optimization

  • NPM | yarn = > lock/flat/cache
  • PNPM => Monorepo/hard, symbolic link/high security…

04. Asynchronous programming

Callback

Promise

Promise is a finite state machine with four states, three of which are Pending, Fulfilled, Rejected and one state that has not started.

Using Promise, the implementation reads the file contents corresponding to the main field in package.json.

Promise solved the problem of callback hell.

Event

Publish subscribe mode, Node.js built-in Events module, such as HTTP Server on(‘request’) event listener

05. Web application development

The HTTP module

Build the simplest HTTP service? Node.js has a built-in HTTP module

const http = require('http'); http.createServer((req,res)=>{ res.end('Hello World\n'); }), listen (3000, () = > {the console. The log (' App running at http://127.0.0.1:3000/ ')})Copy the code

Koa is introduced

Koa – Koa, the next generation Web development framework based on the Node.js platform, not only provides a lightweight and elegant library of functions that makes it easy to write Web applications without binding any middleware to the kernel methods

const app = new Koa(); app.use(async ctx => { ctx.body = 'Hello World'; }); app.listen(3000,() =>{ console.log('App start at http://localost:3000 ... '); })Copy the code

Koa middleware

A Koa application is an object containing a set of middleware functions that are organized and executed according to the Onion model

Koa-based front-end framework

Open source: ThinkJS/Egg… Internal: Turbo, Era, Gulu… What did they do?

  • Koa object response/Request/Context/Application extension
  • Koa common intermediate library
  • Company internal service support
  • Process management
  • The scaffold
  • .

06. Development and debugging

Log debugging – Breakpoint debugging

   npm install ndb -g
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ndb node bootstrap.js

07. Online deployment

Utilize multi-core cpus

The process to protect

Node.js process management tool:

  • Multiple processes
  • Automatic restart
  • Load balancing
  • The log view
  • Performance monitoring
  • .

Complex calculations

conclusion