Node.js fs.readdirSync() Method

The fs.readdirSync() method is used to synchronously read the contents of a given directory. The method returns an array with all the file names or objects in the directory. The options argument can be used to change the format in which the files are returned from the method.

Syntax

fs.readdirSync( path, options )

Parameters: This method accept two parameters as mentioned above and described below:

• path: It holds the path of the directory from where the contents have to be read. It can be a String, Buffer or URL.
• options: It is an object that can be used to specify optional parameters that will affect the method. It has two optional parameters:
  • encoding: It is a string value which specifies which encoding would be used for the filenames given to the callback argument. The default value is 'utf8'.
  • withFileTypes: It is a boolean value which specifies whether the files would be returned as fs.Dirent objects. The default value is 'false'.

Returns: It returns an array of String.

• If withFileTypes is false or not specified: An array of filenames as strings.
• If withFileTypes is true: An array of fs.Dirent objects representing the directory entries.

Features

• Synchronous Execution: fs.readdirSync() is blocking, meaning it halts the execution of subsequent code until the directory contents are read. This is useful when you need to ensure that directory contents are fully read before proceeding.
• Array Output: Returns an array of strings, each representing a file or directory name in the specified directory.
• Optional Encoding: You can specify the encoding (e.g., 'utf8') if you need the results in a specific format.

Below examples illustrate the fs.readdirSync() method in Node.js:

Example 1: This example uses fs.readdirSync() method to return the file names or file objects in the directory.

// Filename - index.js

// Node.js program to demonstrate the
// fs.readdirSync() method

onst fs = require('fs');

// Function to get current filenames
// in the directory
let filenames = fs.readdirSync(__dirname);

console.log("\nCurrent directory filenames:");
filenames.forEach(file => {
  console.log(file);
});

// Function to get current filenames
// in the directory with "withFileTypes"
// set to "true" 
let fileObjs = fs.readdirSync(__dirname, { withFileTypes: true });

console.log("\nCurrent directory files:");
fileObjs.forEach(file => {
  console.log(file);
});

Output:

Current directory filenames:
CONTRUBUTIONS.txt
index.html
index.js
package.json
README.md

Current directory files:
Dirent { name: 'CONTRUBUTIONS.txt', [Symbol(type)]: 1 }
Dirent { name: 'index.html', [Symbol(type)]: 1 }
Dirent { name: 'index.js', [Symbol(type)]: 1 }
Dirent { name: 'package.json', [Symbol(type)]: 1 }
Dirent { name: 'README.md', [Symbol(type)]: 1 }

Example 2: This example uses fs.readdirSync() method to return only the filenames with the ".md" extension.

// Filename  - index.js

// Node.js program to demonstrate the
// fs.readdirSync() method

// Import the filesystem module
const fs = require('fs');
const path = require('path');

// Function to get current filenames
// in directory with specific extension
files = fs.readdirSync(__dirname);

console.log("\nFilenames with the .md extension:");
files.forEach(file => {
  if (path.extname(file) == ".md")
    console.log(file);
})

Output:

Filenames with the .md extension:
README.md

Handling Errors in fs.readdir()

Issues such as incorrect directory paths, insufficient permissions, or inaccessible files can cause errors when using the fs.readdirSync() method. Below are examples of how to handle such errors.

Example:

const fs = require('fs');

// Attempt to read the contents of a non-existent directory
fs.readdir('/invalid/path', (error, fileList) => {
  if (error) {
    // Log the error message if the directory does not exist
    console.error("Error reading directory:", error.message);
  } else {
    // Log the directory contents if no error occurs
    console.log("Files:", fileList);
  }
});

Output:

Error reading directory: ENOENT: no such file or directory, scandir 'C:\invalid\path'

Handling Permission Issues

If the application does not have permission to read a directory, it will throw a permission error. Here’s how you can handle it:

const fs = require('fs');

// Attempt to read a directory without sufficient permissions
fs.readdir('/restricted/path', (error, fileList) => {
  if (error) {
    // Log the permission error
    console.error("Permission error:", error.message);
  } else {
    // Log the directory contents if no error occurs
    console.log("Files:", fileList);
  }
});

Output:

Permission error: ENOENT: no such file or directory, scandir 'C:\restricted\path'

Conclusion

The fs.readdirSync() method is a powerful tool for synchronously reading the contents of a directory in Node.js. It's particularly useful when you need to ensure that directory reading is completed before proceeding with the next steps in your code. While it should be used with caution in scenarios where blocking operations might affect performance, it's an excellent choice for simple tasks and scripts that require immediate and reliable access to directory contents.

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Article Tags :

• Web Technologies
• Node.js
• Node.js-fs-module