Node.js fsPromises.opendir() 方法

fsPromises.opendir()方法在 Node.js 的文件系统模块中定义。文件系统模块基本上是与用户计算机的硬盘进行交互的。该方法用于异步打开目录。
fsPromise.opendir()方法返回一个已解决或被拒绝的承诺，因此避免了 fs.opendir() 中可能发生的回调嵌套或回调地狱问题。承诺通过“fs.Dir”对象解决，该对象本身包含用于访问和关闭目录的其他功能。如果 promise 被拒绝，它将被错误对象拒绝。
句法：

fs.promises.opendir(path, options)

参数：此方法接受上面提到的两个参数，如下所述：

• path：它是一个 String、Buffer 或 Url，用于指定必须打开的目录的路径。
• options：它是一个可选参数，以某种方式影响输出，因此是否将其提供给函数调用。
  • encoding：指定编码技术，默认为 'UTF8'
  • bufferSize：它是一个数字，指定从目录读取时在内部缓冲的目录条目数。 bufferSize 的高值，可确保良好的性能，但会导致更多的内存使用。

返回值：此方法返回一个用 'fs.Dir' 对象解析的承诺，该对象本身包含用于访问和关闭目录的其他函数。如果 promise 被拒绝，它将被错误对象拒绝。
'dir' 对象方法：

• dir.close() 方法：它异步关闭目录的资源，因此后续尝试读取将导致错误。返回一个 Promise，将在资源关闭后解决。
• dir.closeSync() 方法：它同步关闭目录的资源，因此后续尝试读取将导致错误。
• dir.path：返回目录的路径。
• dir.read() 方法：它异步读取下一个目录条目。读取完成后，返回一个 Promise，将使用 fs.Dirent 解析，如果没有更多目录读取，则返回 null。

示例 1：

javascript

// Node.js program to demonstrate the  
// fsPromises.opendir() Method
 
// Importing File System module
const fs = require('fs')
 
fs.promises.opendir('./test1')
    .then(dir => {
        console.log('Directory is opened')
 
        // Path to the directory
        console.log(
        `Path to the directory: ${dir.path}`)
 
        // Closing directory
        return dir.close()
    })
 
    .then(() => {
        console.log('Directory closed')
 
        console.log('\nFurther attempt to'
            + ' read sub-directories\n')
 
        // Further attempt to access the
        // directory results in error
        return dir.read()
    })
 
    .then(dirent => {
 
        // Does not execute since directory
        // is closed catch block runs instead
        console.log(dirent)
    })
    .catch(err => {
        console.log('Error, Something went wrong!')
    })

使用 async-await 实现相同的功能

javascript

// Node.js program to demonstrate the  
// fsPromises.opendir() Method
 
// Importing File System module
const fs = require('fs')
 
const readDir = async (path) => {
 
    // Opeaning directory
    const dir = await fs.promises.opendir(path)
    console.log('Directory is opened')
 
    // Path to the directory
    console.log(`Path to the directory: ${dir.path}`)
 
    // Closing directory
    await dir.close()
    console.log('Directory closed')
 
    console.log('\nFurther attempt '
            + 'to read sub-directories\n')
 
    // Further attempt to access the directory
    // results in error does not execute
    // since directory is closed catch
    // block runs instead
    const subDir = await dir.read()
    console.log(subDir)
}
 
readDir('./test1')
    .catch(err => {
        console.log('Error, Something went wrong!')
    })

输出：

Directory is opened
  Path to the directory: test1
  Directory closed

  Further attempt to read sub-directories

  Error, Something went wrong!

示例 2：

javascript

// Node.js program to demonstrate the  
// fsPromises.opendir() Method
 
// Importing File System module
const fs = require('fs')
 
fs.promises.opendir('./test1')
    .then(dir => {
        console.log('Directory is opened')
 
        // Path to the directory
        console.log(`Path to the directory: ${dir.path}`)
 
        // Reading sub-directories or files
 
        console.log('\nReading sub-directories:\n')
        return dir.read()
    })
 
    .then(dirent => {
        console.log(`Sub-Directory : ${dirent.name}`)
 
        // Reading further sub directories
        return dir.read()
    })
 
    .then(dirent => {
        console.log(`Sub-Directory : ${dirent.name}`)
        return dir.read()
    })
 
    .then(dirent => {
        console.log(`Sub-Directory : ${dirent.name}`)
        return dir.read()
    })
    .then(dirent => {
        console.log(`Sub-Directory : ${dirent.name}`)
        return dir.read()
    })
    .then(dirent => {
        console.log(`Sub-Directory : ${dirent.name}`)
        return dir.read()
    })
    .catch(err => {
        console.log('Error, Something went wrong!')
    })

使用 async-await 实现相同的功能

javascript

// Node.js program to demonstrate the  
// fsPromises.opendir() Method
 
// Importing File System module
const fs = require('fs')
 
const readDir = async (path) => {
 
    // Opeaning directory
    const dir = await fs.promises.opendir(path)
    console.log('Directory is opened')
 
    // Path to the directory
    console.log(`Path to the directory: ${dir.path}`)
 
    // Reading sub-directories or files
    const subDir1 = await dir.read()
    const subDir2 = await dir.read()
    const subDir3 = await dir.read()
    const subDir4 = await dir.read()
    const subDir5 = await dir.read()
 
    // Printing
    console.log(`Sub-Directory : ${subDir1.name}`)
    console.log(`Sub-Directory : ${subDir2.name}`)
    console.log(`Sub-Directory : ${subDir3.name}`)
    console.log(`Sub-Directory : ${subDir4.name}`)
    console.log(`Sub-Directory : ${subDir5.name}`)
}
 
readDir('./test1')
    .catch(err => {
        console.log('Error, Something went wrong!')
    })

输出：

Directory is opened
  Path to the directory: test1

  Reading sub-directories:

  Sub-Directory : example1.txt
  Sub-Directory : example2.txt
  Sub-Directory : example3.txt
  Sub-Directory : example4.txt
  Sub-Directory : null

参考： https://nodejs.org/dist/latest-v14.x/docs/api/fs.html#fs_fspromises_opendir_path_options