What is the Purpose of __filename Variable in Node.js ?

In Node.js, there are several global variables that are available in all modules. One such variable is __filename. This article delves into the purpose, usage, and practical applications of the __filename variable in Node.js.

What is __filename?

The __filename variable is a built-in global variable in Node.js that provides the absolute path of the file that is currently being executed. Unlike other global objects, __filename is not a function, but a variable that holds a string value representing the file's full path.

Syntax:

console.log(__filename)

Return Value:

It returns the absolute filename of the current module.

Characteristics of __filename:

• Global Scope: __filename is accessible from anywhere within the module without the need to import or require it.
• Module-Specific: It always refers to the current file in which it is used, meaning that each module has its own __filename value.
• Absolute Path: The value of __filename is the absolute path, meaning it includes the complete directory structure leading to the file.

Purpose of __filename

The primary purpose of __filename is to provide the absolute path of the current module's file, which can be used for various tasks in Node.js applications, such as:

• File Operations: Reading or writing files relative to the current file's location.
• Dynamic Path Resolution: Constructing paths dynamically for use in importing modules or other file-based operations.
• Logging: Including the current file's path in logs or error messages for better debugging and tracing.
• Meta Programming: Obtaining metadata about the current file for tasks such as code generation or module introspection.

Installation Steps

Step 1: Make a folder structure for the project.

mkdir myapp

Step 2: Navigate to the project directory

cd myapp

Step 3: Initialize the NodeJs project inside the myapp folder.

npm init -y

Project Structure:

Example 1: Implementation to show the use of __filename variable in Node.js

// app.js

console.log("GeeksforGeeks");
console.log("Name of the file which we"
    + " are currently executing is  ");
console.log(__filename)

Step to Run Application: Run the application using the following command from the root directory of the project

node app.js

Example 2: In this example, we will use split function to split the directory returned by __filename.

// app.js

console.log("GeeksforGeeks");

// To show to parts of file using filename.
const parts = __filename.split(/[\\/]/)
console.log( "This the all the parts "
    + "present in file :",parts);

Step to Run Application: Run the application using the following command from the root directory of the projectOutput:

node app.js

Example 3: In this example, we will simply display the filename not the directory. Firstly, we will get the directory using __filename then split it. Then we will print the last index of the split array.

// app.js

console.log("GeeksforGeeks");
// To show exact name of the file.
const parts = __filename.split(/[\\/]/)
console.log( "FileName is : " + parts[parts.length-1]);

Step to Run Application: Run the application using the following command from the root directory of the project

node app.js