This article explains the FS file module and path module in nodejs in detail

1. First time to know  Node.js

In the browser  JavaScript  Component part

Why?  JavaScript  Can be executed in the browser

Different browsers use different  JavaScript  Parsing engine

Chrome  browser => V8

Firefox  browser => OdinMonkey（ Odin monkey ）

Safri browser => JSCore

IE  browser => Chakra（ chakra ）

among ,Chrome  Browser's  V8  The parsing engine has the best performance ！

Why?  JavaScript  Can operate  DOM  and  BOM

Every browser has built-in  DOM、BOM  In this way  API  function , therefore , In the browser  JavaScript  Before you can call them

In the browser  JavaScript  Running environment

Running environment

It refers to the necessary environment for the normal operation of the code

summary

• V8  The engine is responsible for parsing and executing  JavaScript  Code

• built-in  API  It is a special interface provided by the operating environment , Can only be called in the running environment

JavaScript  Can you do back-end development

need node.js

Node.js  brief introduction

• What is?  Node.jsNode.js  It's based on  Chrome V8  Engine  
  JavaScript  Running environment
  Official website address  https://nodejs.org/zh-cn/

• Node.js  Medium  JavaScript  Running environment

• Browser is  JavaScript  The front end running environment of

• Node.js  yes  JavaScript  The back end running environment of

• Node.js  Cannot call  DOM  and  BOM  Browser built in  API

• Node.js  What can be done

Node.js  As a  JavaScript  Operating environment , It only provides basic functions and  API. However , be based on  Node.js  These foundations can , Many powerful tools and frameworks have sprung up , Emerge in endlessly , So I learned  Node.js , It can make front-end programmers competent for more jobs and posts

• a be based on  Express  frame  http://www.expressjs.com.cn/  You can quickly build  Web  application

• b be based on  Electron  frame  https://electronjs.org/  Can build cross platform desktop applications

• c be based on  restify  frame  http://restify.com/  You can quickly build  API  Interface project

• d Read, write and operate the database 、 Create practical command line tools to assist front-end development 、etc…

• Node.js  How to learn

• In the browser  JavaScript  Learning path

• JavaScript  Basic grammar  +  Browser built in  API（DOM + BOM） +  Third party Library （jQuery、art-template  etc. ）

• Node.js  The learning path of JavaScript  Basic grammar  + Node.js  built-in  API（fs、path、http etc. ）+  The third party  API  modular （express、mysql  etc. ）

shift+ Right mouse button   You can open it in this directory powershell window

stay powershell Shortcut key in ：

• , You can quickly navigate to the last command executed .

• tab key
  , You can quickly complete the path of the file （ First enter the first word , And then use tab key , Can quickly complete the path ）

• ESC
  , You can quickly clear the entered commands

• cls
  , Empty powershell panel

tips：./ Represents the current directory , You can write it or not

2.fs  File system module

What is?  fs  File system module

fs  The module is  Node.js  Official 、 A module used to manipulate files . Provides a series of methods and properties , It is used to meet the operation requirements of files. If you want to  JavaScript  In the code , Use  fs  Module to manipulate files , You need to import it first in the following way

const fs = require("fs")


fs.readFile(path[, option], callback)

Read the contents of the specified file

path

Required parameters , character string , File path

option

Optional parameters , Set character set

callback

Required parameters , Callback function after reading the file

// 1.  Import  fs  modular , To manipulate the file
const fs = require('fs')

// 2.  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 , Generally, it is specified by default  utf8
//  Parameters 3： Callback function , Get the results of reading failure and success  err dataStr
fs.readFile('./files/1.txt', 'utf8', function(err, dataStr) {
 
 // 2.1  Print failed results
 //  If the read is successful , be  err  The value of is  null
 //  If the read fails , be  err  The value of is   Error object ,dataStr  The value of is  undefined
 console.log(err)
 console.log('-------')
 
 // 2.2  Print successful results
 console.log(dataStr)
})
// General logic can be written like this ：
fs.readFile('./files/11.txt', 'utf8', function(err, dataStr) {
 if (err) {
 return console.log(' Failed to read file ！' + err.message)
 }
 console.log(' Read file successful ！' + dataStr)
})


fs.writeFile(path, data[, option], callback)

Write content to the specified file

path

Required parameters , character string , File path

data

Required parameters , Written content

option

Optional parameters , Set character set , The default value is  utf8

callback

Required parameters , Callback function after file writing

Be careful ： Writing will overwrite the original content

const fs = require('fs')

// 2.  call  fs.writeFile()  Method , Write the contents of the file
//  Parameters 1： Indicates the storage path of the file
//  Parameters 2： Indicates what to write
//  Parameters 3： Callback function
fs.writeFile('./files/3.txt', 'ok123', function(err) {
 // 2.1  If the file is written successfully , be  err  The value is equal to the  null
 // 2.2  If the file fails to write , be  err  The value of is equal to a   Error object
 // console.log(err)
// Judge whether the writing is successful
 if (err) {
 return console.log(' File write failed ！' + err.message)
 }
 console.log(' File written successfully ！')
})


Omitting the third parameter defaults to UTF8 Format

Preface ： The problem of path dynamic splicing

Use fs Module operation file , If the operation path provided is in ./ or ../ At the beginning

Relative paths

when , It is easy to have the problem of path dynamic splicing error . reason ： When the code is running ,

Will be executed in node The directory where the command is located

, Dynamically splice the complete path of the operated file . Solution : In the use of fs Module operation file ,

Provide a complete path directly

, Don't offer . or ../ The relative path at the beginning , So as to prevent the problem of path dynamic splicing . Be careful js Write the full path in //, Otherwise, it will be treated as an escape character .** But this method has poor portability .fs There are solutions in .

__dirname

  Indicates the directory where the current file is located （ That is to js The location of the document is the benchmark ）

, Will not open according to node The catalogue changes

（ Open node Is the benchmark ）.

console.log(__dirname)

fs.readFile(__dirname + '/files/1.txt', 'utf8', function(err, dataStr) {
 if (err) {
 return console.log(' Failed to read file ！' + err.message)
 }
 console.log(' Read file successful ！' + dataStr)
})


3.path  Path module

path  The module is  Node.js  Official 、 The module used to process the path . Provides a series of methods and properties , It is used to meet the processing requirements of the path. If you want to  JavaScript  In the code , Use  path  Module to handle the path , You need to import it first in the following way

const path = require("path")


path.join(...paths)

  Multiple path fragments can be spliced into a complete path string

• ...paths <string> Sequence of path fragments

• return  
  <string>
  Be careful ： All operations involving path splicing , All use  path.join()  Methods to deal with . Don't use + String splicing

const path = require('path')
const fs = require('fs')

//  Be careful ： ../  Will offset the previous path
const pathStr = path.join('/a', '/b/c', '../../', './d', 'e')
console.log(pathStr) // \a\b\d\e

//  replace fs.readFile(__dirname + '/files/1.txt', ...)
fs.readFile(path.join(__dirname, './files/1.txt'), 'utf8', function(err, dataStr) {
 if (err) {
 return console.log(err.message)
 }
 console.log(dataStr)
})


path.basename(path[, ext])

  You can get the last part of the path , This method is often used to obtain the file name in the path

• path <string>
  Required parameters , A string representing a path

• ext <string>
  Optional parameters , Represents the file extension

• return  <string> The last part of the path

const path = require('path')

//  Define the storage path of the file
const fpath = '/a/b/c/index.html'

const fullName = path.basename(fpath)
console.log(fullName) // index.html

const nameWithoutExt = path.basename(fpath, '.html')
console.log(nameWithoutExt) // index


path.extname(path)

  You can get the extension part of the path

• path <string> Required parameters , A string representing a path

• return  <string> Return the obtained extension string

const path = require('path')

//  This is the storage path of the file
const fpath = '/a/b/c/index.html'

const fext = path.extname(fpath)
console.log(fext)// Output .html


Be careful ：

fs.writeFile() Method can only be used to create files , Cannot be used to create path repeat calls fs.writeFile( Write to the same file , The newly written content will overwrite the previous old content