This article will take you through the operation of reading and writing files in Nodejs

How to operate files in

Node? The following article will talk about how to use Nodejs to read and write files. I hope it will be helpful to you!

# Manipulating files is a basic function of the server and one of the necessary capabilities for back-end development.

Operating files mainly includes reading and writing. These functions Nodejs have already provided corresponding methods. Just call it.

Create folder

Synchronization method

const fs = require('fs')
fs.mkdirSync(`${__dirname}/雷猴`)

NodeJS There is a file module called fs . To operate on files, this module must be introduced first.

Use the fs.mkdirSync method to create a folder. Just enter the name of the folder to be created.

__dirname refers to the absolute path of the folder where the current file is located.

Asynchronous creation

const fs = require('fs')
fs.mkdir(`${__dirname}/雷猴`, err => {
  if (err) {
      console.error(err)
  }
})

Use the fs.mkdir method to create asynchronously. The first parameter is also the folder name, and the second is Back to the function, there is a err parameter in this function, which can return error information.

Delete files

After creating the folder, I originally wanted to talk about "delete the folder". However, since all the files in the folder must be cleared before deleting it, the usage of Deleting files will be discussed first.

There are two ways to delete files: synchronous and asynchronous.

Synchronization fs.unlinkSync

const fs = require('fs')
fs.unlinkSync(`${__dirname}/test.txt`);

fs.unlinkSync Input the path and file name of the file to be deleted to delete the specified file.

Asynchronous fs.unlink

const fs = require('fs')
fs.unlink(`${__dirname}/test.txt`, err => {
  if (err) {
      console.error(err)
  }
})

fs.unlink The method has 2 parameters. The first parameter is the file path and file name. The second parameter is the callback function that monitors deletion failure.

Delete Folder

Before deleting a folder, clear all files in the target folder. Files can be deleted using fs.unlinkSync or fs.unlink.

Sync

const fs = require('fs')
fs.rmdirSync(`${__dirname}/雷猴`)

Asynchronous

const fs = require('fs')
fs.rmdir(`${__dirname}/雷猴`, err => {
  if (err) {
      console.error(err)
  }
})

The usage is similar to deleting files. There are also synchronous and asynchronous methods for deleting folders. , accepts 2 parameters asynchronously, and the second parameter is also a callback for monitoring error reports.

Write data

const fs = require('fs')
const content = ' 雷猴雷猴\n'
const opt = {
  flag: 'a', // a：追加写入；w：覆盖写入
}

fs.writeFile('test.txt', content, opt, (err) => {
  if (err) {
      console.error(err)
  }
})

fs.writeFile method can write content to a file. If the file does not exist, it will be automatically created.

fs.writeFile Parameter description:

• First parameter: file name
• Second parameter: written content
• The third parameter: writing mode (append, overwrite, etc.)
• The fourth parameter: error message monitoring

Reading data

const fs = require('fs')
fs.readFile('fileName', (err, data) => {
  if (err) {
      console.error(err)    
      return
  }  
  // data 是二进制类型，需要转换成字符串  
  console.log(data.toString())
})

Use the fs.readFile method to read data. The first parameter is the file name; the second parameter is the callback, err monitors error messages, data is the data read back.

It should be noted that the data read back is a binary type of data, which needs to be converted into data we can understand using the toString() method.

Check whether the file exists

const fs = require('fs')
const exist = fs.existsSync('fileName')
console.log(exist)

Use the fs.existsSync method to check whether the specified file exists, and return true# if it exists. ## ; Otherwise, return false.

Summary

NodeJS as the backend, you cannot escape the knowledge of reading and writing files. Its most common function can write logs, such as collecting error logs, etc.

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