How To Use __dirname in Node.js

Introduction

__dirname is an environment variable that tells you the absolute path of the directory containing the currently executing file.
In this article, you will explore how to implement __dirname in your Node.js project.

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Prerequisites

To complete this tutorial, you will need:

A general knowledge of Node.js. To learn more about Node.js, check out our How To Code in Node.js series.

This tutorial was verified with Node.js v17.2.0 and npm v8.2.0.

Step 1 — Setting Up the Project

This tutorial will use the following sample directory structure to explore how __dirname works:

dirname-example
  ├──index.js
  ├──public
  ├──src
  │  ├──helpers.js
  │  └──api
  │      └──controller.js
  ├──cronjobs
  │  └──hello.js
  └──package.json

You can start by creating a dirname-example directory in your terminal:

mkdir dirname-example

Navigate to the project directory:

cd dirname-example

Initialize it as a Node.js project:

npm init --yes

Now, you will create the directories and files to experiment with.

Step 2 — Using __dirname

You can use __dirname to check on which directories your files live.
Create and edit controller.js in the api subdirectory in the src directory:
src/api/controller.js

console.log(__dirname)      // "/Users/Sam/dirname-example/src/api"
console.log(process.cwd())  // "/Users/Sam/dirname-example"

Then, run the script:

node src/api/controller.js

Create and edit hello.js in the cronjobs directory:
cronjobs/hello.js

console.log(__dirname)     // "/Users/Sam/dirname-example/cronjobs"
console.log(process.cwd()) // "/Users/Sam/dirname-example"

Then, run the script:

node cronjobs/hello.js

Notice that __dirname has a different value depending on which file you console it out. The process.cwd() method also returns a value, but the project directory instead. The __dirname variable always returns the absolute path of where your files live.

Step 3 — Working With Directories

In this section, you will explore how to use __dirname to make new directories, point to them, as well as add new files.

Making New Directories

To create a new directory in your index.js file, insert __dirname as the first argument to path.join() and the name of the new directory as the second:
index.js

const fs = require('fs');
const path = require('path');
const dirPath = path.join(__dirname, '/pictures');

fs.mkdirSync(dirPath);

Now you’ve created a new directory, pictures, after calling on the mdirSync() method, which contains __dirname as the absolute path.

Pointing to Directories

Another unique feature is its ability to point to directories. In your index.js file, declare a variable and pass in the value of __dirname as the first argument in path.join(), and your directory containing static files as the second:
index.js

express.static(path.join(__dirname, '/public'));

Here, you’re telling Node.js to use __dirname to point to the public directory that contains static files.

Adding Files to a Directory

You may also add files to an existing directory. In your index.js file, declare a variable and include __dirname as the first argument and the file you want to add as the second:
index.js

const fs = require('fs');
const path = require('path');
const filePath = path.join(__dirname, '/pictures');

fs.openSync(filePath, 'hello.jpeg');

Using the openSync() method will add the file if it does not exist within your directory.

Conclusion

Node.js provides a way for you to make and point to directories. And add files to existing directories with a modular environment variable.
For further reading, check out the Node.js documentation for __dirname, and the tutorial on using __dirname in the Express.js framework.