__dirname, module Paths & import.meta.url

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__dirname and Module Paths

In CommonJS, Node.js injects __dirname (the directory of the current file) and __filename (the full file path) into every module. These are essential for building paths that work regardless of where your script is called from.

// CommonJS
const path = require("path");

console.log(__filename); // /home/user/app/index.js
console.log(__dirname);  // /home/user/app

const configPath = path.join(__dirname, "config", "app.json");
console.log(configPath); // /home/user/app/config/app.json

ESM Equivalent

ESM does not provide __dirname. Use import.meta.url together with the url and path modules to recreate it.

// ESM
import { fileURLToPath } from "url";
import { dirname, join } from "path";

const __filename = fileURLToPath(import.meta.url);
const __dirname = dirname(__filename);

const configPath = join(__dirname, "config", "app.json");
console.log(configPath);

Always build file paths with path.join rather than string concatenation to ensure cross-platform compatibility on Windows, macOS, and Linux.

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