An article explaining in detail how to read and write files in Nodejs

Operating 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. Nodejs has already provided corresponding methods for these functions. Just call it.

Create folder

synchronization method

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

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

A folder can be created using the fs.mkdirSync method. 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.

Asynchronously create

const fs = require('fs')
fs.mkdir(`${__dirname}/Thunder Monkey`, 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 parameter is the return function. There is an err parameter in this function, which can return error information.

deleting files

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

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

Synchronize fs.unlinkSync

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

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

asynchronous fs.unlink

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

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

Delete a folder

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

Synchronous

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

asynchronous

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

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

Write data

const fs = require('fs')
const content = 'Thunder MonkeyThunder Monkeyn'
const opt ​​= {
  flag: 'a', // a: append writing; w: overwrite writing}

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

The 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
• third parameter: writing mode (append, overwrite, etc.)
• fourth parameter: error message monitoring

read data

const fs = require('fs')
fs.readFile('fileName', (err, data) => {
  if (err) {
      console.error(err)    
      return
  }  
  // data is a binary type and needs to be converted into a string 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 information, and data is the read data.

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

Check if the file exists

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

uses the fs.existsSync method to detect whether the specified file exists. If it exists, it returns true ; otherwise, it returns false .

Summary:

If you use 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.

We can also write logs in the database, but not all computers have the same database installed. But if you write the log in a file, the contents of the file can generally be easily opened on other computers.