Node.js fsPromises.opendir()用法及代碼示例

fsPromises.opendir()方法在Node.js的文件係統模塊中定義。文件係統模塊本質上是用於與用戶計算機的硬盤進行交互的。該方法用於異步打開目錄。

fsPromise.opendir()方法返回已解決或被拒絕的諾言，因此避免了fs.opendir()中可能發生的回調嵌套或回調地獄問題。承諾通過“ fs.Dir”對象解析，該對象本身包含其他用於訪問和關閉目錄的函數。如果諾言被拒絕，它將被錯誤對象拒絕。

用法:

fs.promises.opendir(path, options)

參數：該方法接受上述和以下所述的兩個參數：

path:它是一個String，Buffer或Url，它指定必須打開的目錄的路徑。
options:它是一個可選參數，它會以某種方式影響輸出，因此會相應地將其提供給函數調用。
- encoding:它指定了編碼技術，默認為“ UTF8”
- bufferSize:它是一個數字，指定當從目錄讀取時在內部緩衝的目錄條目的數量。 bufferSize的值較高，可以確保良好的性能，但會導致更多的內存使用。

返回值：該方法返回一個用“ fs.Dir”對象解析的promise，該對象本身包含其他用於訪問和關閉目錄的函數。如果諾言被拒絕，它將被錯誤對象拒絕。

‘dir’對象方法：

dir.close()方法：它異步關閉目錄的資源，因此，後續嘗試讀取將導致錯誤。返回一個Promise，將在資源關閉後解決。
dir.closeSync()方法：它同步關閉目錄的資源，因此，後續嘗試讀取將導致錯誤。
dir.path：返回目錄的路徑。
dir.read()方法：它異步讀取下一個目錄條目。讀取完成後，將返回一個Promise，將使用fs.Dirent進行解析；如果沒有更多的目錄讀取，則返回null。

範例1：

// 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 attemp 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實現相同的函數

// 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 attemp 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!') 
    })

輸出：

  Directory is opened
  Path to the directory:test1
  Directory closed

  Further attempt to read sub-directories

  Error, Something went wrong!

範例2：

// 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實現相同的函數

// 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!') 
    })

輸出：

  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

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

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注：本文由純淨天空篩選整理自hunter__js大神的英文原創作品 Node.js | fsPromises.opendir() Method。非經特殊聲明，原始代碼版權歸原作者所有，本譯文未經允許或授權，請勿轉載或複製。