NodeJS - readdirSync() method explained

The readdirSync() from the fs module allows you to read a folder’s content using NodeJS. The method will list all filenames inside the folder as an array and return them to you for further operations.

The method `read accepts the following 2 parameters:

• path to the directory - string (required)
• options to affect the method return value - object (optional)

The options parameter allows you to pass additional parameters as follows:

• encoding - specifies the encoding used for the filenames returned by readdirSync()
• withFileTypes - The returned array will contain Dirent objects instead of just a string

The following code example will read the content of the current directory or folder and log the file names to the console:

const fs = require("fs");

const files = fs.readdirSync(__dirname);

console.log(files); // Log the content of the current folder

When you need to retrieve the content of a specific folder, you can pass the path to the folder as a string. The code below will look into the assets folder, which is right inside the current folder:

const fs = require("fs");

const path = "./assets";

const files = fs.readdirSync(path);

console.log(files); // Log the content of assets folder

When you set the withFileTypes option to true, the method will return an array of Dirent objects as follows:

const fs = require("fs");

const files = fs.readdirSync(__dirname, { withFileTypes: true });

console.log(files); 

[
  Dirent { name: '.DS_Store', [Symbol(type)]: 1 },
  Dirent { name: 'assets', [Symbol(type)]: 2 },
  Dirent { name: 'index.html', [Symbol(type)]: 1 },
  Dirent { name: 'index.js', [Symbol(type)]: 1 },
  Dirent { name: 'read.js', [Symbol(type)]: 1 },
  Dirent { name: 'vue.png', [Symbol(type)]: 1 }
]

Unfortunately, the Dirent object doesn’t have the file types property where you can check for a specific type. When you need to return only specific file types, you can use a combination of array filter() method and extname() method from the path module.

First, read the folder without passing any option. Then, use the filter() method on the returned array and return only files with the specified extension.

For example, the code below will return only files with .js extension in my current folder:

const fs = require("fs");
const path = require("path");

const files = fs.readdirSync(__dirname);

const jsFiles = files.filter(function (file) {
  return path.extname(file) === ".js";
});

console.log("The following files are using .js extension: ");
console.log(jsFiles); // [ 'index.js', 'read.js' ]

By using fs.readdirSync() method, you can easily read the content of any folder located in your filesystem.