Node.js Installation and introduction

1. use nvm management node edition

In general, when studying , A version of node That's enough , You can download it directly on the official website . But in the production process , It's hard to avoid meeting node For different versions of the project , So download nvm It's a necessary thing . If it is windows user , Please use nvm-windows！

https://github.com/nvm-sh/nvm/blob/master/README.md

install ：

curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.1/install.sh | bash

Add related configuration ,nvm The default location is ~/.nvm.

export NVM_DIR="$([ -z "${XDG_CONFIG_HOME-}" ] && printf %s "${HOME}/.nvm" || printf %s "${XDG_CONFIG_HOME}/nvm")"
[ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh" # This loads nvm

After the above two lines are run , Passing instructions nvm list You can see mvn Installed node Version list . If the installation is successful, you can display .

Install the specified node edition ： For example, the large version to be installed is 16 Of , direct nvm install 16 that will do . The small version is the same nvm install 16.15.0.

Switch to another version node： Switch the large version number directly nvm use 14, You can switch to the large version 14 Of node Environmental Science , The same is true for specifying small versions .

View the currently used node edition ：node -v

2. nodejs and js The difference between

• ECMAScript（ES）： Defines the syntax , Write JS and nodejs Must abide by
  • Variable definitions , loop , Judge , function
  • Prototypes and prototype chains , Scope and closure 、 asynchronous
  • Can't operate DOM, Can't monitor click Time , Can't send Ajax request
  • Can't handle http request , Can't operate file
  • therefore , Only ES, I can hardly do any actual projects
• JavaScript（JS）： Use ES Grammatical norms , Plus Web API, Be short of one cannot .Web API Standard by W3C Regulations .
  • DOM operation ,BOM operation , Time bound ,Ajax etc.
  • Combination of the two , You can complete any operation on the browser side
• nodejs： Use ES Grammatical norms , Plus nodejs API.
  • Handle http, Processing documents, etc
  • Combination of the two , Can finish server Any operation on the end

summary

• ECMAScript It's grammar
• nodejs = ECMAScript + nodejs API
• JS = ECMAScript + WebAPI

function nodejs Method

Command line run ：

node js File path 

that will do , Also available vscode Plugins in Code Runner, One click operation , Save your own manual input command line .

3. commonjs

commonjs Import and export

// a.js
function add(a, b) {
    
  return a + b;
}

function mul(a, b) {
    
  return a * b;
}

module.exports = {
    
  add,
  mul,
};

// b.js
const {
     add, mul } = require("./a");

const sum = add(10, 20);
const mulRes = mul(100, 200);

console.log(sum);
console.log(mulRes);

commonjs quote npm package

Initialization first npm Download after environment npm package

yarn init -y
yarn add lodash

And then according to npm Name reference is enough

const _ = require("lodash");

const arr = _.concat([1, 2], 3);
console.log(arr); // [1, 2, 3]

4. debugger

debugger Everyone is familiar , The code pauses at the break point , Easy to find errors .

vscode stay debug When , I'll look for package.json Of main Property , This file is the main entry , The default name is index.js.

After the break point, you can click the debugging entry on the left to start debugging .

5. server The difference between development and front-end development

Not learned nodejs It means that we can develop the back-end ！

• Service stability
  • server The client may suffer from various malicious attacks and misoperations
  • A single client can hang up unexpectedly , But the server cannot
  • Service stability application ：PM2 Process daemons
• Consider memory and CPU （ Optimize , Expand ）
  • The client monopolizes one browser , Memory and CPU It's not a problem
  • server The end has to carry many demands ,CPU And memory are scarce resources
  • Use stream Write the log , Use redis save session, Optimize memory
• logging
  • The front end will also participate in logging , But only the initiator of the log , Don't care about follow-up
  • server The client should record the log 、 Store logs 、 Analysis log , The front end doesn't care
• Security
  • server The client should be ready to receive all kinds of malicious attacks at any time , The front end is much less , Such as ： Unauthorized operation , Database attacks, etc
  • application ： validate logon , The prevention of xss Attack and sql Inject
• Cluster and service splitting
  • Fast product development , Traffic may increase rapidly
  • Carry more traffic by expanding machine and service splitting