Detailed explanation of nodejs

node.js

1. install nodejs

   https://nodejs.org/zh-cn/
   

2. Package manager npm

   npm init  initialization 
   npm install  Download dependency  && npm install  Download dependency @ Version number  // Installation package  
   -S -save  Abbreviation   Used in the production of （ go online ） In the environment , The package name will be registered in package.json Of dependencies Inside , In the production environment, the dependency of this package still exists ;
   -D -dev（ production ）  The package name will be registered in package.json Of devDependencies Inside , Packages that exist only in the development environment -D, Such as babel,sass-loader These parsers 
   devDependencies , These are some packages that we need to use when developing , It only needs to be used in the development phase , You don't need these packages when you really pack them online , Because these tools are just what you use to package code , Is used to identify specific files and codes , Help us produce the final documents 
   dependencies, This needs to be released to the production environment , For example, if you want to run a race based on vue Project , So we need to vue.js To support , And this vue.js Documents need to follow the project to the final production environment 
   
   -g  Global installation 
   npm uninstall  Package name  // Uninstall package 
   npm run  Run the project 
   

3. nrm

   nrm ls // Check the optional download source 
   nrm use name // Switch download source 
   nrm add registry  Download source  // Add download source 
   nrm del name // Delete download source 
   nrm test// Test Download response time 
   

4. nvm management node edition

   nvm list available // List all the... That can be installed node edition 
   nvm install 17.2.0  //node Version number download 
   nvm ls // Show downloaded node edition   Front belt * Is currently in use node edition 
   nvm use 17.2.0 // Use node edition 
   

5. npx

   npx @vue/cli -V amount to npm install @vue/cli -g   +  vue -V
   1、 Temporarily install executable dependent packages , No global installation , Don't worry about long-term pollution .
   2、 You can execute commands in dependent packages , The installation is complete and runs automatically .
   npx create-react-app my-react-app // Download to the temporary directory and delete it automatically after use 
   3、 Automatic loading node_modules Dependent packages in , Don't have to specify $PATH.
   node-modules/.bin/mocha --version
   npx mocha --version
   4、 You can specify node edition 、 The version of the command , It solves the problem that different projects use different versions of commands .
   npx [email protected] -v
   

6. modularization

    Three ways to export modules 
   module.exports = {
   	function add(a,b){}
   		return a+b
   	}
   	console.log(add(1,2))
   }
   
   module.exports.name = 'zs'
   exports.num = 18
   
    Use require The import module 
   const index = require('./index');
   

7. fs modular

   fs.readFile(path[,options],callback)
   fs.writeFile(path,' Content ',callback)
   
   //  Import fs
   const fs = require('fs')
   
   //  call fs.writeFile() Method write file 
   //  Parameters 1: Write the storage path of the file 
   //  Parameters 2: Write the contents of the file , The format is generally utf8
   //  Parameters 3： Callback function 
   fs.writeFile('./node.txt','asdfsaf',function (err) {
   	if (err) {
   		return console.log(' File write failed ',err.message);
   	}
   	console.log(' File written successfully ');
    })
   
    //  call fs.readFile() Method to read the file 
   //  Parameters 1: Read the storage path of the file 
   //  Parameters 2: The encoding format used when reading the file , It's usually utf8
   //  Parameters 3： Callback function , Get the results of failure and success 
   fs.readFile('./node.txt','utf8',function (err,succeed) {
   	if (err) {
   		return console.log(' File read failed ',err);
   	}
   	console.log(' The content of the document is ：',succeed);
    })
   

8. dirname

   //__dirname Indicates the directory where the current file is located 
   console.log(__dirname);
   // Output E:\nodeStudy
    It can be used __dirname+'./node.txt' Splicing file path 
   

9. path modular

   path.join() // Splicing file path 
   path.basename()  // Get the file name in the file path 
   path.extname()	// Get the file extension name in the path 
   
   // Import path modular 
   const path = require("path")
   
   const pathStr = path.join('a','b','c','..','d/f')
   console.log(pathStr);//a\b\d\f
   
   path.join(__dirname+'/node.txt')// Splicing file path 
   
   path.fpath = 'a/b/c/index.html'
   console.log(path.basename(fpath))// Get the file name index.html
   console.log(path.basename(fpath,'.html'))// Get the file name prefix index
   
   console.log(path.extname(fpath))//.html
   

10. http modular

    //  Import http modular 
    const http = require("http")
    //  establish web Server instance 
    const serve = http.createServer()
    //  Bind to the server instance request event , Listen for client requests 
    // req For the object of the request , Contains data and properties related to the client 
    //res The response object , It contains data and attributes related to the server 
    serve.on('request',(req,res)=>{
    	console.log(req.url,req.method);
    	console.log('request event ');
    	res.setHeader("Content-Type","text/html;charset=utf-8");// If you do not set the encoding format and use Chinese, the code will be garbled 
    	res.end(" The request successfully returned data ")
    })
    //  Start the server 
    serve.listen(8088,()=>{
    	console.log(" Server started successfully :http://127.0.0.1:8088");
    })