A brief analysis of common modules in node: path module and fs module

There are many built-in objects in node, which can help us perform many operations, including operations on paths, files, etc. The following article will introduce to you the path module and fs module among the commonly used built-in modules of node. I hope it will be helpful to you!

path module

The path module is used to process paths and files and provides many methods.

path.resolve

There is a requirement to concatenate the path and file name.

const basePath = '/user/why'
const filename = 'abc.txt'

Then someone will use string splicing to splice.

const filePath = basePath + '/' + filename
console.log(filePath);

Although there is no problem with this result, considering different systems, Windows systems can use \ or \\ or / as path separators, while Mac OS and Linux Unix operating systems use / as path separators. symbol.

To solve the above problem, we can use path.resolve to splice paths.

const path = require('path')

const basePath = '/user/why'
const filename = 'abc.txt'

const filePath = path.resolve(basePath, filename)

console.log(filePath);

Get information from path

• dirname: Get the parent folder of the file
• basename: Get file name
• extname: Get file extension

const path = require('path')

const filePath = '/User/haha/abc.txt'

console.log(path.dirname(filePath));
console.log(path.basename(filePath));
console.log(path.extname(filePath));

Path splicing

If we want to splice multiple paths, but different operating systems may use different separators, we can use the path.join function.

const path = require('path')

const basepath = '/User/haha'
const filename = 'abc.txt'

const filePath = path.join(basepath, filename)
console.log(filePath);

Splice a file and a folder

If we want to splice a file and a folder, we can Use path.resolve.

const basepath = 'User/haha'
const filename = 'abc.txt'

path.resolve and path.join can also be used to splice paths, so what is their difference?

const basepath = '../User/haha'
const filename = './abc.txt'
const othername = './haha.js'

const filePath1 = path.join(basepath, filename, othername)
console.log(filePath1);

const filePath2 = path.resolve(basepath, filename, othername)
console.log(filePath2);

We can see the difference.

fs module

nodejs Most file system APIs provide three operating methods:

• Synchronous file operation: the code will be blocked and will not continue to execute

• Asynchronous callback function file operation: the code will not be blocked and a callback needs to be passed in function, when the result is obtained, the callback function executes

• Asynchronous Promise operation file: the code will not be blocked. Calling method operation through fs.promises will return a Promise, which can be passed then , catch for processing.

Read file status (information)

Method 1 synchronization operation: fs.statSync

const fs = require('fs')

const filepath = './abc.txt'
const info = fs.statSync(filepath)
console.log('后续需要执行的代码');
console.log(info);

Method 2 asynchronous operation

fs.stat(filepath, (err, info) => {
  if(err) {
    console.log(err);
    return
  }
  console.log(info);
  console.log(info.isFile()); // 判断是否是一个文件
  console.log(info.isDirectory()); // 判断是否是一个文件夹
})
console.log('后续需要执行的代码');

Method 3: Promise

fs.promises.stat(filepath).then(info => {
  console.log(info);
}).catch(err => {
  console.log(err);
})

console.log('后续需要执行的代码');

File descriptor

node is allocated for all open files A file descriptor of type numeric. All file system operations use these file descriptors to identify and track each specific file.

fs.open() method is used to allocate a new file descriptor fd. Once allocated, the file descriptor can be used to read data from the file, write data to the file, or request information about the file.

const fs = require('fs')

fs.open('./abc.txt', (err, fd) => {
  if(err) {
    console.log(err);
    return
  }

  // 通过文件描述符去获取文件信息
  fs.fstat(fd, (err, info) => {
    console.log(info);
  })
})

File reading and writing

fs.readFile(path[, options], callback): Read file content

fs.writeFile( path[, options], callback): Write content to the file

option parameters:

flag: Writing method

encoding: Character encoding

Writing of files

fs.writeFile('./abc.txt', content, {flag: "a"}, err => {
  console.log(err);
})

Reading of files

fs.readFile('./abc.txt', (err, data) => {
  console.log(data);
})

If encoding is not filled in, the result Buffer (binary) will be returned.

fs.readFile('./abc.txt', {encoding: 'utf-8'}, (err, data) => {
  console.log(data);
})

Create a folder

Use fs.mkdir() or fs.mkdirSync Create a new folder.

const fs = require('fs')

// 创建文件夹
const dirname = './haha'
if(!fs.existsSync(dirname)) {
  fs.mkdir(dirname, (err) => {
    console.log(err);
  })
}

Get the contents of the folder

fs.readdir

fs.readdir(dirname, (err, files) => {
  console.log(files);
})

Get all the files in the folder. The directory is as shown below, Recursion can be used.

const fs = require('fs')
const path = require('path')
const dirname = './haha'

function getFiles(dirname) {
  fs.readdir(dirname, {withFileTypes: true}, (err, files) => {
    // console.log(files);
    for(let file of files) {
      // 判断是否是文件夹
      if(file.isDirectory()) {
        const filepath = path.resolve(dirname, file.name)
        getFiles(filepath)
      } else {
        console.log(file.name);
      }
    }
  })
}

getFiles(dirname)

重命名

可以使用fs.rename对文件夹进行重命名。

fs.rename('./haha', './xixi', err => {
  console.log(err);
})

更多node相关知识，请访问：nodejs 教程！

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