Node.js Command Line Usage
Node.js provides a powerful command line interface (CLI) that allows you to run JavaScript files, manage packages, debug applications, and more.
This guide covers the essential commands and techniques every Node.js developer should know.
Note: All commands should be run in a terminal or command prompt.
On Windows, you can use Command Prompt, PowerShell, or Windows Terminal.
On macOS/Linux, use Terminal.
Basic Node.js Commands
These are the most common commands you'll use when working with Node.js applications:
Run a JavaScript file
# Run a JavaScript file
node app.js
# Run with additional arguments
node app.js arg1 arg2
# Run in watch mode (restarts on file changes)
node --watch app.js
Using the REPL
The Node.js REPL (Read-Eval-Print Loop) is an interactive shell for executing JavaScript code.
The REPL is started by running node in the terminal:
Using the REPL
> const name = 'Node.js';
> console.log(`Hello, ${name}!`);
> .help // Show available commands
> .exit // Exit REPL
Command Line Arguments
Access command line arguments using process.argv:
Command Line Arguments
// args.js
console.log('All arguments:', process.argv);
console.log('First argument:', process.argv[2]);
console.log('Second argument:', process.argv[3]);
// Example usage:
// node args.js hello world
// Output:
// All arguments: ['/path/to/node', '/path/to/args.js', 'hello', 'world']
// First argument: hello
// Second argument: world
Environment Variables
Access and set environment variables:
Environment Variables
// env.js
console.log('Environment:', process.env.NODE_ENV || 'development');
console.log('Custom variable:', process.env.MY_VARIABLE);
console.log('Database URL:', process.env.DATABASE_URL || 'Not set');
// Example usage with environment variables:
// NODE_ENV=production MY_VARIABLE=test node env.js
Set Environment Variables
# Set environment variables when running
NODE_ENV=production MY_VARIABLE=test node env.js
Debugging Node.js Applications
Node.js includes a powerful debugging system that integrates with Chrome DevTools:
Basic Debugging Commands
# Start with inspector (listens on default port 9229)
node --inspect app.js
# Break on first line of application
node --inspect-brk app.js
# Specify a custom port
node --inspect=9222 app.js
# Enable remote debugging (be careful with this in production)
node --inspect=0.0.0.0:9229 app.js
Using Chrome DevTools for Debugging
- Start your application with
node --inspect app.js - Open Chrome and navigate to
chrome://inspect - Click on "Open dedicated DevTools for Node"
- Set breakpoints and debug your application
Common CLI Tools
Node.js comes with several useful command-line tools:
Node Version Manager (nvm)
# Install and use different Node.js versions
nvm install 18.16.0 # Install specific version
nvm use 18.16.0 # Switch to version
nvm ls # List installed versions
npm (Node Package Manager)
# Common npm commands
npm init # Initialize a new project
npm install # Install dependencies
npm update # Update packages
npm audit # Check for vulnerabilities
Common Command Line Flags
Node.js provides several command-line flags to control its behavior. Here are some of the most useful ones:
Basic Flags
# Show Node.js version
node --version # or -v
# Show V8 version
node --v8-options
# Show command-line help
node --help
Runtime Behavior
# Check syntax without executing
node --check app.js
# Show stack traces for warnings
node --trace-warnings app.js
# Set max memory (in MB)
node --max-old-space-size=4096 app.js
# Preload a module before execution
node --require dotenv/config app.js
Performance and Optimization
# Enable ES module loader
node --experimental-modules app.mjs
# Enable experimental features
node --experimental-repl-await
# Enable experimental worker threads
node --experimental-worker
