02-globals.md

Overview

In Node.js, there are global objects and variables that are available in every module without needing to import them. Unlike browser JavaScript which has the window object, Node.js provides its own set of globals designed for server-side development.

Key Node.js Globals

1. __dirname - Current Directory Path

console.log(__dirname)

What it does: Returns the absolute path of the current directory containing the currently executing file.

Example output:

/Users/username/projects/node-express-course/01-node-tutorial

Common use cases:

• Reading files relative to the current directory
• Setting up file paths for asset serving
• Constructing dynamic paths for logging

Example:

const path = require('path');
const filePath = path.join(__dirname, 'data', 'users.json');

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2. __filename - Current File Name

What it does: Returns the absolute file path of the currently executing file.

Example output:

/Users/username/projects/node-express-course/01-node-tutorial/02-globals.js

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3. require() - Module System Function

What it does: Allows you to import modules using the CommonJS module system.

Example:

const express = require('express');
const fs = require('fs');
const path = require('path');

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4. module - Current Module Information

What it does: Contains information about the current module, including exports and other metadata.

Example:

console.log(module)
// Shows: { exports: {}, ...other properties }

module.exports = { name: 'My Module' };

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5. process - Environment Information

What it does: Provides information about the Node.js process and environment variables.

Common properties:

process.env       // Environment variables
process.argv      // Command-line arguments
process.cwd()     // Current working directory
process.exit()    // Exit the process
process.version   // Node.js version

Example:

console.log(process.env.NODE_ENV);  // 'development' or 'production'
console.log(process.argv);           // Array of command-line arguments

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Practical Example: setInterval

The code also demonstrates setInterval(), a global function for running code repeatedly:

setInterval(() => {
  console.log('hello world')
}, 1000)

What it does: Runs the callback function every 1000 milliseconds (1 second).

Output:

hello world
hello world
hello world
... (repeats indefinitely)

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Complete Working Example

// Display current directory and file
console.log('Current directory:', __dirname);
console.log('Current file:', __filename);

// Run a function every 1 second
let count = 0;
setInterval(() => {
  count++;
  console.log(`[${count}] hello world`);
  
  // Stop after 5 iterations
  if (count === 5) {
    process.exit(0);  // Use process.exit() to terminate
  }
}, 1000);

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Key Differences from Browser JavaScript

Browser	Node.js
window global	global global
document available	No DOM
Can't access file system directly	fs module for file access
No __dirname or __filename	Both available automatically
process not available	process always available

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Summary

Node.js globals are essential for:

• ✅ Working with file paths (__dirname, __filename)
• ✅ Managing modules (require, module)
• ✅ Accessing environment configuration (process)
• ✅ Creating timers and intervals (setInterval, setTimeout)

These globals make it easy to build server-side applications without needing to import everything explicitly!